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MODEL 

AEROPLANES 

The Building of Model Monoplanes, 
Biplanes, etc., together with a 
Chapter on Building a Model Airship 




BY 


F. J. C4MM 

\\ 


WITH 190 ILLUSTRATIONS 


NEW YORK 

FUNK & WAGNALLS COMPANY 


















^, '’f'l / 





I 




EDITOR’S PREFACE 


cC 

& 

This is a practical handbook on the principles, con¬ 
structional details and methods of building model 
aeroplanes, written by a well-known model aeroplane 
designer and builder. It deals with every part of a 
machine and describes a number of different types, in¬ 
cluding monoplanes, biplanes, collapsible machines, 
tractor monoplanes, hydro-monoplanes, aeroplanes 
driven by compressed air, etc., etc. The concluding 
chapter explains how to build a model airship, and, as 
in the case of all the others, is based on the results of 
practical experience. Readers in need of further in¬ 
formation on the subject should address their inquiries 
to “Work,” La Belle Sauvage, London, E.C., through 
whose columns (but not by post), assistance will be 
gladly given. 


B. E. J. 


♦ 

CONTENTS 

CHAPTER, PAGE 

1. Why an Aeroplane Flies * . . . 1 

2. Types of Model Aeroplanes . . .12 

3. Practical Construction : Model Aeroplane 

Fuselages . . . . . .19 

4. Practical Construction : Carving Air-screws 35 

5. Practical Construction : Bending Air-screws 42 

6. Practical Construction : Planes . . 47 

7. Simple Twin-screw Monoplane . . 54 

8. Simple Twin-screw Biplane ... 61 

9. Winders for Elastic Motors ... 69 

10. Collapsible Monoplane .... 73 

11. Tractor Monoplane ..... 80 

12. Hydro-Monoplane ..... 87 

13. Compressed-air Engine for Model Aeroplane 94 

14. Biplane Driven by Compressed-air Engine 104 

15. General Notes on Model Designing . .120 

16. General Notes.124 

17. Easily Made Tailless Kites . . .136 

18. Building a Model Airship ... 141 

Index. 154 






MODEL AEROPLANES 


CHAPTER I 

Why an Aeroplane Flies 

Why does an aeroplane fly? The question is 
worthy of close examination. There is one common 
enemy to aeroplanes—the force of gravity. Were it 




Fig. 1.—Bristol Monoplane and Biplane 

1 















MODEL AEROPLANES 


not for the existence of this force, which, as Newton 
put it, “is unseen and unheard and yet dominates 
the universe,” the problem of the aeroplane would 

have been solved years ago. 

Most readers have handled the toy kite, and since 
the principles governing the flight of a kite are pre¬ 
cisely the same as those which apply to the aeroplane, 
the latter will be the more readily understood if the 
principles are explained through this medium. Full- 



Fig. lA. —Forces Acting on Kite 


size aeroplanes to which certain models approximate 
are shown in Fig. 1. 

If a kite is launched in a wind it speedily attains 
a certain height or altitude, at which it remains so long 
as the wind does not drop. The wind is overcoming 
gravity, which constantly endeavours to bring the kite 
to earth, and hence, since the kite remains in the air, 
the forces acting on the kite are said to be in equili¬ 
brium—that is, balanced. The forces are shown 
diagrammatically in Fig. 1a, and include gravity, which 
is practically constant and remains unaltered under 
all conditions, the air pressure which, when sufficiently 
intense, lifts the kite against the action of gravity, 





WHY AN AEROPLANE FLIES 


*> 


and the pull of the string. The air pressure is really 
a combination of two forces—lift and drift. The drift 
or resistance tends to move the kite in the direction 
of the wind, and lift to raise the kite in opposition to 
gravity. Since, therefore, drift is an undesirable 
factor, the resistance of the machine must be made as 
low as possible, as it absorbs power, as will clearly be 
seen. If the velocity of the wind drops, the kite drops 
also, increasing its angle with the horizon, thereby 
causing it to capture and force down more air until 
equilibrium is again restored. If the string of a kite 
breaks, the balance of the forces is destroyed, drift 
and gravity taking command and so bringing the kite 
to earth. 

If it takes a wind of fifteen miles an hour to lift 
a kite, similarly it would lift to exactly the same 
elevation if the holder of the kite-string commenced 
to run at a rate of fifteen miles per hour in calm air. 

Now, an aeroplane is merely a kite with a 
mechanical arrangement (the engine and propeller) 
which supplies the motion necessary to fly it, and 
eliminates the necessity for a wind. This statement 
can easily be followed. In the aforementioned parallel 
it was seen that it was immaterial whether the kite- 
flyer was standing still with the wind moving at fifteen 
miles per hour, or whether he was moving at the rate 
of fifteen miles per hour in still ail\ The result in 
each case is the same—the kite flies. 

It has been stated that if the kite-string fractured 
the kite would fall to the ground. If, however, it 
were possible at the moment of rupture to attach a 



4 


MODEL AEROPLANES 


weightless engine and airscrew to the kite capable of 
exerting a forward push equal to the drift, the kite 
would still remain in the air. 

Again, if the wind were suddenly to stop, and 
the engine and airscrew were capable of moving the 
kite forward at the same rate at which the wind was 
blowing, the kite would lly, and in all important 
respects would constitute an aeroplane. 

The kite, it will be assumed, requires a minimum 
speed of fifteen miles per hour in order to sustain 
itself. If the wind be blowing at fifteen miles an 
hour the operator can remain stationary. If it blows 
at ten miles an hour he must run at five miles an hour 
against the wind. If it blows at five miles an hour 
he must run at ten miles an hour against the wind, 
or twenty miles per hour with the wind to maintain 
the kite. 

Hence an aeroplane really has two speeds—its 
speed relative to the earth and its air speed. The 
former is the rate of which it w r ould travel a given 
distance, and the latter is the sum of the speed rela¬ 
tive to the earth and the velocity of the wind. 

It can readily be seen that an aeroplane travelling 
at ten miles an hour relative to the earth against a 
fifteen-mile-an-hour wind has really an air speed of 
twenty-five miles an hour. When the aeroplane, how¬ 
ever, is travelling with the wind, the air speed is the 
speed relative to the earth minus the velocity of the 
wind. 

It is also convenient to draw a parallel between 
the ship and the aeroplane. The weight of a ship 





WHY AN AEROPLANE FLIES 


5 


must equal the weight of water it displaces in order 
to float. Similarly an aeroplane, by its motion 
through the air, must deflect a volume of air equal at 
least to its own weight. The aeroplane then would 
just lift itself from the ground; and the more air it 
deflects the higher does it ascend. 

Now, if a 1-lb. weight be laid on a table, the table 
presses against the weight with a force of 1 lb. If 
the hand is pressed against the wall, the wall presses 



back with an equal pressure. If a person hres a re¬ 
volver, the force of explosion tends to force the 
revolver and the person in the opposite direction to 
the travel of the bullet. These are merely illustrations 
of the law that action and reaction are equal and 
opposite. It is in reality due to this law that the 
aeroplane can resist gravity. 

Fig. 2 represents an end view of a kite—or, for 
that matter, of an aeroplane. The arrows indicate 
the direction of motion of the wind. Upon contact 
with the kite the air has a downward action, and the 















6 


MODEL AEROPLANES 


consequent reaction lifts the kite. Hence the motion 
of an aeroplane through the air causes a pressure on 
the latter, and the resultant is what is termed lift. 

So far, then, the reason why an aeroplane lifts 
has been dealt with. Further considerations have to 
be dealt with after the machine has left the ground. 
In technical language these could be summarised into 
a single sentence—that is, the centres of pressure and 
gravity must be made to coincide, and the machine 


■*—- s" -- 



1 

t 

\ 

Centye of Pressures C.Gr.f 


-.O- to: 


Centres of Pressure And b-ra vi , 


Fig. 3.—Position of Centre of Gravity 

must also be stable in both lateral and longitudinal 
directions. 

An ordinary paper glider, cut from a stiff sheet 
of cartridge paper, will serve admirably to demonstrate 
this statement, which at first sight will convey as 
much to the reader as Choctaw or other remote 
language. 

Cut the paper to the dimensions given in Fig. 3. 
and make sure that it is flat, by pressing between 
the leaves of a book. Then project it horizontally 
into the air. It does not attain gliding motion. It 





















WHY AN AEROPLANE FLIES 


7 


performs a series of evolutions, too quickly for the 
eye to perceive; but what happens is this. After 
launching, the front edge turns up and the sheet glides 
back. Now the back edge turns up and the glider 
dives forward. Again the front edge turns up, the 
glider slides back, the back edge turns up, it glides 
forward, and so on until the glider reaches the ground. 
Now fix a couple of small brass paper-fasteners in the 
front edge (the correct number of fasteners can how¬ 
ever only be found by experiment, but two will usually 
be sufficient for the size of glider indicated), and launch 
the glider again. It will be noticed that it glides 
steadily at a small angle to the ground. 

The explanation of this phenomenon is simple. 
When it was launched in the first place, the centre 
of gravity of the plane lay along a line running 
through the geometrical centre, parallel with the front 
edge, and the glider merely rocked or oscillated about 
this axis. The centre of pressure of the surface would 
be approximately in the position shown in the illus¬ 
tration. When the correct number of paper-fasteners, 
however, are fixed, the centre of gravity is moved 
forward to a position coincident with the centre of 
pressure, the result being that the glider came to 
earth in steadiness and poise. But, even though it is 
now balanced, it will still show a tendency to rock 
sidewise or laterally, and if.the wings-are bowed up 
to the dihedral angle shown in Fig. 4, the rock will 
be eliminated, and the machine is said to be laterally 
stable. Either of the dihedral angles may be used, 
although b is much to be preferred, 



8 


MODEL AEROPLANES 


What of stability in a longitudinal direction? Just 
as important this, but not quite so easy to obtain. 

Fig. 5 is a side elevation of two surfaces fixed tG 
a spar, and shows how stability is obtained longi¬ 
tudinally. The surfaces of the elevator or tail, ac¬ 
cording to whether the machine is “canard” or 
tractor (canard being the term for propeller behind or 
“pusher” machines), is placed at a positive angle 
with the horizon. The correct angle can, of course, 
only be found by experiment. 

Now, from the foregoing certain laws can be de¬ 
duced. Firstly, in order to be stable longitudinally.. 



c 

Fig. 4.—Various Forms of Dihedral 


the centre of pressure must be kept as near to the 
centre of gravity as possible, and secondly, the main 
surface of the aeroplane must be inclined to preserve 
lateral stability. With full-size aeroplanes there are, 
however, several exceptions to this rule, as the faster 
a machine travels the more stable does it become, 
and hence the dihedral angle is really unnecessary. 

It may be well at this point to describe the action 
of a plane. Strictly speaking, the terms “plane” 
and “ aeroplane ” are misnomers, since no full-size 
machine has surfaces which even approximate to 
planes. 




Fig. 5.—Disposition of Angles 


i On of Dead Air 



Fig. 6.—Air-flow Round Plane 



Fig. 7.—Air-flow Round Cambered Surface 



Fig. 8.—Air-flow Round Streamline Strut 


on of dead Air 





P'ig. 9.—Air-flow Round Square. Strut. 


^ * 'W~ 



























10 


MODEL AEROPLANES 


The reason why a perfectly flat plane is never used 
on full-size aeroplanes will be followed from Fig. 6. 
which shows the flow of air over an inclined plane, 
the term “plane ” being used here in its technical 
sense. 

It will be noticed that a region of “dead air ” or 
partial vacuum is caused, which seriously affects the 
lift of the plane. Fig. 7 shows the flow of air ovei 
a cambered aerofoil (or to use the popular collo¬ 
quialism “ plane ”). Less disturbance occurs in this 



instance, the air following very approximately the 
contour of the surface. It has been proved by test in 
the Wind Tunnel at the National Physical Laboratory 
at Teddington that an efficiently-designed aerofoil 
section has a lift two-thirds greater than a true plane. 
For a similar reason all struts or aeroplanes are 
streamlined,” as shown by Fig. 8. The air flow, 
it will be seen, is less disturbed than by a square strut 
(Fig. 9). 

Fig. 10 shows the air Sow round a square-ended 
and taper-ended plane respectively. It will be noticed 
that the air has a tendency to leak over the end of 































WHY AN AEROPLANE FLIES 


ii 


the square plane, which is obviated by the tapered 

wing. 

It may be thought that such details as these are 
unimportant; but when it is remembered that an aero¬ 
plane, correctly streamlined, will fly for one-half the 
power required to fly a machine not so designed, the 
enormous saving in power will be manifest. 

The actual thrust required to lift a model aeroplane 
is roughly equal to a quarter of its total weight. Thus 
a model weighing 6 oz. will require lj-oz. thrust. 



CHAPTER II 


Types of Model Aeroplanes 

#• 

With a view to illustrating some of the models 
described in this book complete, some drawings are 
given of the more successful designs which have come 
into prominence during the past eight years. Fig. 11 
shows the Ridley Monoplane, which secured several 
well-merited rewards in open competition, and is an 
excellent machine for distance. Birch should be used 
for the longerons, preferably of channelled section. 
The main plane is of piano wire, covered with proofed 
silk, and the elevator is entirely of extremely thin 
veneer. Bentwood screws are used fairly short in 
diameter and of long pitch. The machine is capable 
of flying a quarter of a mile. The Fairey type of model 
aeroplane typified in Fig. 12 is a most successful type, 
and has achieved much in open competition. It has 
vvhat is known as a floating tail, with no leading 
stabilising surface, but a small vertical fin is used. 
This is a practice the writer is not personally in favour 
of, as through such a long lever -the slightest wind 
will cause great instability. If a vane or fin must be 
used, it should be placed as far to the rear of the 
machine as possible, preferably just behind, or in 
front of the propellers for pusher machines, and the 
extreme end of the tail for the tractor type. 


TYPES OF MODEL AEROPLANES 


13 


The swept-back wing tips should have a negative 
angle of about tw r o degrees, and the tail should be 
quite flat in relation to the horizontal. 



It has been stated that this machine is a highly 
successful one; it is also exceedingly intricate in ad¬ 
justment, and requires very calm weather indeed to 


B 









14 


MODEL AEROPLANES 


secure successful flights. It has also been flown w 7 ith 
great success by Mr. Houlberg, who at one time held 
the official duration record of 89 secs. w T ith his 
machine. The long unrelieved length of spar pro¬ 
jecting forward of the main surface detracts much 
from its appearance in the air. A machine of this 
type should not weigh more than 8 oz. ? and 
is capable of a flight of at least a minute in duration 
The simple 1-1-P 1 type drawn in Fig. 13 w T as 
formerly popularised by Mr. T. W. Iv. Clarke, of 
Kingston, who used all-wooderi surfaces, a solid spar 
and bentwood screw built up in two halves. This 
method of screw manufacture is unique, since if 
enables the two blades to be prepared from jigs to a 
greater degree of accuracy than when it is bent from 
one piece. Moreover, the lapping of the two halved 
at the boss imparts strength to the boss where it is 
most needed. Fig. 14 is a type of tractor monoplane 
very successful for duration, capable of doing a minute 
at an altitude of forty feet. The rudder of tractor 
machines must always be placed above the thrust line 
and also above the centre of gravity, so that should 
a side gust strike the machine, the latter does not 
rock laterally in the air, as a couple is set up between 
the underhung load and the rudder. 

The winner of the Wakefield Gold Challenge Cup 
is shown in Fig. ]5. It was designed by Mr. E. W. 
Twining, one of the early experimenters, for duration, 
and in the winning flight scored a duration of sixty-five 
seconds. It is a very pretty and stable flyer, and will 
rise from the ground after a run of about five feet. 




TYPES OF MODEL AEROPLANES 15 


Fig. 16 is of the Bragg-Smith biplane, which first 
came into prominence at Wembley in 1909. The 
original machine was a huge machine some four feet 



Fig. 14.— 
Tractor 
Monoplane 


Fig. 15.—Twining Monoplane 


Fig. 16.—Bragg- 
Smith Biplane 


in span, possessing a propeller of large diameter, large 
blades, and large pitch—quite the antithesis to 
ordinary practice. Latterly, however, Mr. Smith has 











































TYPES OF MODEL AEROPLANES 17 


developed his machines into twin-screw, and no doubt 
is entertained that even better results are obtained 
with this arrangement. 

It should be pointed out, in passing, that this 
machine is the subject of a patent for stability, it 
being claimed that greater lateral stability is obtain¬ 
able from the curved lower main-plane. A sketch is 



also given in Fig. 17 of a tractor hydro-biplane. This 
should weigh about 12 ozs. finished. The tandem 
monoplane shown by Fig. 18 is another machine which 
has scored many successes in the early days of model 
aeroplaning at the Crystal Palace. Figs. 19, 20, 21, 22 
show the Twining hand-launched biplane, a tractor 
biplane built by the writer, a fuselage biplane (canard 











18 MODEL AEROPLANES 


or screw behind), and a Bleriot type tractor mono¬ 
plane. 

A tractor machine is one having the screw in front, 
and a “canard ” or “pusher ” machine has its screw 
behind. It is best to designate the machine by the 
type formula. Thus, a pusher monoplane with twin 
screws would be a l-l-P 2 -0 type. If it had a tail it 
would be 1-1-P 2 -1.' A twin-screw “pusher” biplane 
with or without tail would be l-2-I )2 -l and l-2-P 2 -0 
respectively. A pusher monoplane with only one 
screw is a 1-1-P 1 type. A tractor monoplane with 
single screw is P l -1-1; a tractor biplane with single 
screw is P x -2-l. If a biplane tail is also used it be¬ 
comes P 1 -2-2. If twin screws are used it would then 
become P 2 -2-2, and so on. 



CHAPTER III 


Practical Construction: Model Aeroplane 

Fuselages 

Ln no other portion of a model aeroplane lias 
standardisation become more marked than in the 
design and construction of the fuselage or main frame, 
both with regard to general details, methods, and 
materials. This fact is singular, because in other 
components contributing in a greater degree to the 
success of the model great diversity of opinion exists. 
It is difficult to ascribe this lack of uniformity to any 
particular reason, unless it is the failure on the part 
of zealous amateurs to appreciate the meaning of the 
term “ efficiency.” Very few, it is thought, endeavour 
to extract the maximum amount of work for a mini 
mum expenditure of powder from the propellers, sur¬ 
faces, and so forth, and the writer, in judging and 
tabulating some of the model aeroplane competitions 
held in different parts of the country, has found 
models giving excellent spectacular results which, 
judged on an efficiency basis, such as 

distance flown x duration of flight, 
weight of rubber 

show a very poor result. The model should be made 




20 


MODEL AEROPLANES 


to fly the longest possible distance, and to remain in 
the air tlie longest possible time with the smallest 

possible amount of elastic. 

This chapter is devoted to the various types ol 
fuselage for flying models (as distinct from “ scale 
models of full-size prototypes) and methods of con¬ 
structing them, and the list is as representative of 
best practice as it has been possible for the writer, in 
his extensive connection with this subject, to make it. 

The first shown is the A frame (Fig. 23), brought 
into prominence by Mr. It. F. Mann. It should have 
birch longitudinals and spruce cross members. Quite 
the best section wood to employ is that shown at B. 
which forms a convenient seating for the cross mem¬ 
bers, the latter being pinned and glued into position. 
The middle bay of such a frame requires to be braced, 
to counteract the torque or distortion caused by the 
elastic skein when the latter is in torsion. Diagram A 
shows the joint at the juncture of the longerons oi 
longitudinals. The hooks which embrace the elastic 
skeins are formed from one continuous length of wire 
following round the nose of the machine. The bear¬ 
ings may be of brass, with a lug to follow round the 
end of the longeron to which it is bound. 

Fig. 24 shows the T or cantilever frame, so 
named because of its resemblance to that letter. It 
is usual to make the spar of this hollow, by channelling 
out two pieces of wood, and gluing and cramping 
them together under pressure. Where the bracing 
kingpost passes through the channel should be packed, 
previous to gluing the two half spars together, with a 





















































22 


MODEL AEROPLANES 


piece of hard wood, so that the assembled spar is not 
weakened by the piercing necessary for the insertion 
of the kingpost. Such a spar should not exceed 4 ft 
in length, c is a section of the spar. 

A much stronger twin-screw fuselage, which is 
a combination of the A and T frames, is shown by 
Fig. 25. Here, again, a single-channelled longeron 
should be used, although the propeller bar. and sup 
ports should be solid. The channelled spar can be 
of silver spruce or birch, and the bar and supports of 
mahogany. A section of the spar is given at D. 

Fig. 26 shows a T frame made from a hollow spar, 
having the ends splayed out to give the required sup¬ 
port to the elastic skein. No propeller bar* is used 
but there is a tension wire from bearing to bearing 
to prevent the splayed section of the spar from spread 
ing when the rubber is wound up. e shows a section 
of the spar. It should be pointed out that the greatest 
width of a spar should be placed vertically. Never 
use a square-sectioned spar. Moreover, the bearing 
centres should only exceed the propeller diameter by 
J in., since, apart from consideration of weight, greater 
rigidity is obtainable from short spars than from long 
ones. It is in details such as this that not only is a 
considerable saving in weight effected, but also a 
material increase in strength and efficiency. 

The T frame adapted to a “ rise-off-ground 
fuselage is shown in Fig. 27. A hollow spar should 
be used for preference, but the spar cut from the solid 
is shown, as most amateurs will not be in possession 
of a joiner’s plough, which is the tool required for 





of Fuselage AW — 
































24 


MODEL AEROPLANES 


this job. F is a section on the vertical line of the 
spar. 

In bracing such frames as those dealt with, fine 
No. 35 s.w.G. (Standard Wire Gauge) should be used, 
fixed to small hooks hound in suitable places on the 
spar; the hooks should he made from No. 22 s.w.G. 

Fig. 27 shows at G a perspective view of a T-frame 
propeller bar and support. As there shown, the pro¬ 
peller bar fits into a slot cut in the spar end. If the 
spar is hollow, the channel should be filled with 
hard wood, such as birch, before the slot is cut, to 
strengthen the spar at this point. So much for twin- 
screw fuselages. 

Fig. 28 is a perspective view of a boat-shaped 
tractor fuselage, it being understood that a tractor 
machine is one with the airscrew in front. A model 
built on such lines is extremely neat in appearance 
and has a pleasing aspect in the air. The three 
longerons ape attached to a three-way brass bearing 
at the front end, and are simply bound together at 
the rear, the hook for the elastic being inserted be¬ 
tween the two top members and turned round the end 
of one of them for security, as shown at H. The 
bottom member should be cut 1 in. longer than the 
two top ones, to compensate for the shortening due 
to the curve, which is effected by compressing the 
bottom member to the same length as the top ones. 
The curved cross members are of bamboo, bent to the 
required shape over a lamp flame; or they could be 
made from piano wire. Their shape should be drawn 
full size to use as a tenlplate during the bending 




MODEL AEROPLANE FUSELAGES 25 


operation. As will be seen, a skid is used to protect 
the tractor screw from damage. This should extend 
for 2 in. beyond the bearing, and must be attached 
to the bottom longitudinal directly beneath the first 
cross member, so that the latter absorbs the shock of 
landing. At the point of intersection between the 
skid and the axle, the former should be bound to the 
latter with fine florist’s wire and neatly soldered. 

A two-membered fuselage can be adapted from this 
design by omitting the bottom member and skid. Such 
a fuselage would be suitable for a light machine. 

It is an essential point with tractor models to fit 
a chassis: the purpose thus being twofold. First, 
it protects the propeller, and secondly, it obviates the 
characteristic tendency of tractor machines to ascend 
“ nose first,” by keeping the weight low (in technical 
language, providing a low centre of gravity). Hand- 
launched tractor machines that are unprovided with a 
landing gear are seldom successful and notoriously 
troublesome. Furthermore, the centre of thrust 
(literally the axis centre, or centre of rotation of the 
bearing) should always be above the centre of resist¬ 
ance. The centre of resistance can usually be taken 
(although not quite accurate) as being on a level with 
the planes. 

An exceedingly strong two-membered tractor 
fuselage of the fusiform or cigar-shaped type is that 
shown by Fig. 29, the bearing, which is bracketed and 
cut from brass, being shown in detail at 1 . In this 
instance the greatest width of the top spar should be 
disposed horizontally, the bottom member, with the 



26 


MODEL AEROPLANES 


two cross members, providing rigidity and a girder¬ 
like form of construction. The bottom member need 
be only one-half the weight of the top one, as it will 
be in tension and so acting as a tie. Silver spruce 
should be used throughout. 

A simple single-spar chassis, consisting of a hollow 
spar, is shown by Fig. 30. A kingpost and bracing 
is fitted underneath the spar, to counteract the ten¬ 
dency of the twisted skein to bow it. The chassis 
should be (and this applies to all models) of piano 
wire of from No. 17 s.w.g. to No. 18 s.w.G. 

A twin-screw propeller-behind fuselage of the can¬ 
tilever type that is exceedingly strong, although more 
difficult than it appears to construct, is shown by 
Fig. 31. This can be made exceedingly light from 
a hollow spar (packed solid at the point where the 
kingposts are let through), and braced with No. 35 
s.w.g. piano wire. The bracing is the difficult opera¬ 
tion, as the tension on each wire requires to be very 
delicately adjusted to maintain the truth of the spar. 

The box-girder type of fuselage shown by Fig. 32 
is more suited to models which aim at an accurate 
representation of some prototype. It is intricate in 
construction yet of neat appearance, the difficulty 
being in the adjustment of the large number of brac¬ 
ing wires necessary. The illustration gives a view cf 
a Bleriot type of fuselage, J being a detail of the cross 
member and compression-strut joint. 

Fig. 33 gives some spar sections which are in 
common use by some of the crack aero-modellists. All 
spars should taper in a fore-and-aft direction, so that it 



3>des Covered With Thm l/c.neer 



of Fuselage 









































































28 


MODEL AEROPLANES 


virtually becomes a cantilever. The greatest cross 
section should be one-third of the total length from 
the front end of the spar. 

Another form of spar construction is that given by 
Fig. 34. Q shows a spar fretted out, the sides being 
covered with a thin veneer glued and cramped into 
place, and k the method of making a slotted spar. 

Fig. 35 is the simplest possible form of model aero¬ 
plane fuselage, if such it can be called. 

Choice of materials and the method of utilising 
them to the best advantage, so that the machine is 
strong without being unduly heavy, is a phase of 
model aeroplaning that calls for some care and judg¬ 
ment. There is a very erroneous impression prevalent 
among novices that packing-case wood or similar 
material is suited to the requirements peculiar to model 
aeroplanes. Nothing could be farther from the truth ; 
and the fact that 50 per cent, of the total marks 
awarded in competition are for design and construc¬ 
tion should show that this matter is of primary im- 
portance. The true test of any model is the way it 
stands up ” to a nose dive, for then the care and 
forethought of the builder in providing for anticipated 
eventualities will manifest itself. It is to be feared 
that those who had lavished much care and infinite 
pains in the scientific construction of models were 

t 

woefully handicapped in competition, the flimsy freak 
that could flutter aloft for a minute or so, with three 
strands of rubber wound to nearly breaking point, 
gaining priority over the properly built machine. 

There are three salient paints .to he borne in mind 



MODEL AEROPLANE FUSELAGES 29 


on which the durability of the machine largely* de¬ 
pends : (1) its capacity for resisting the torque of the 
rubber motor; (2) of absorbing the shocks of rough 
landing; and (3) the provision that has been made 
for the rigid attachment of.the various parts. If the 
machine is at fault with regard to point one, fuselage 
distortion is likely to occur, and resulting from this 
there will be lack of alignment of the surfaces and 
attendant troubles. Point two calls for suitable brac¬ 
ing of the spar or spars, and careful choice of timber. 
It is inadvisable to use wood of square cross-section, 



Fig. 35.—Simple Fuselage 


an oblong section with the greatest measurement 
placed vertically being preferable. If no arrangement 
has been made to fix rigidly the wings, chassis, etc. 
(point 3), these parts are likely to rock or sway when 
the machine is in the air, and so occasion bad stability, 
apart from which a couple of landings would shake 
the machine out of truth. 

To obviate these difficulties a knowledge of the 
strength of the various timbers will be found useful, 
and there is appended a table of the weights of various 
timbers. The writer prefers birch for fuselage mem¬ 
bers over 3 ft. 6 in. in length. Although on the heavy 
side compared with spruce, it will stand a great 
amount of rough usage. Spruce is also suitable for 
c 












30 


MODEL AEROPLANES 


fuselages up to this length, while maple is more suited 
for main planes. Bamboo can be used more effica¬ 
ciously for cross members, struts, etc. Some model- 
makers use bamboo for planes, the joint of the rib to 
the spar being by means of glue and cross-binding. 
Although planes so built are exceedingly strong, it is 
not possible to make quite so neat a job of them as 
with spruce or maple. 

Another method of building main planes is to use 
spruce or birch spars with piano-wire ribs, these latter 
being bound to the former. 

Bor single-spar models the main spar should be 

tapered fore and aft from a point one-third of the 

length from the front of the machine. Where it is 

necessary to pierce the spar of a model aeroplane for 

the reception of a kingpost or other member, silk tape 

binding should be used, the joint being soaked with 

clean, weak glue. 

- * 

To resist fuselage distortion the spar must be suit¬ 
ably braced in a lateral direction, the outrigger carry¬ 
ing the bracing wires being situated just forward of 
the centre of the spar. No. 35 s.w.G. is quite strong 
enough for fuselage bracing. Silk fishing-line or 
Japanese silk gut is admirably suited for wing brac¬ 
ing, and is not so liable to stretch as the tinned-iron 
or brass wire sometimes used. Piano wire is generally 
used for elevators, tail planes, chassis, and propeller 
shafts, of a gauge ranging from No. 17 s.w.G. to 
No. 22 s.w.G. A clock-spring or piano-wire protector 
fitted tQ;the nose of a model aeroplane will also prevent 
a broken spar should it strike any object during flight. 





Fig. 38a.—Twin-screw Bearings 






















3 2 


MODEL AEROPLANES 


'!' 


Weight 

of Woods Chiefly 

Used 


Mahogany 

. 35 lb. per 

cubic 

foot 

Birch 

. 45 


) ? 

Maple 

... •... 46 

y ’ 

5 > 

Spruce ... 

. 31 

y > 

5 ) 

Bamboo 

. 25 

y •> 



Building Scale Models.—Models of well-known 
machines should be built to correct proportions, if as 
perfect a resemblance as possible is aimed at. The 
best way to do this is, of course, to adopt a definite 
scale. The particular scale will depend principally 
on the size the builder requires his model; but the 
size of the prototype must, of course, be considered, 
because the large machines differ so much in point of 
size. 

Taking the span or width across the planes as 
the base from which to start, it is assumed that the 
width of the model is desired to be from 25 in. to 
35 in., which is perhaps the best all-round minimum 
and maximum to adopt. Then having decided on the 
prototype, multiply the span of the real machine by a 
fraction, which brings the model span somewhere be¬ 
tween the two figures. For instance, suppose it is 
desired to model an Antoinette monoplane, the span 
of which is about 46 ft., and multiplying by § the 
model ..span becomes 34J; therefore the scale is J in. 
to the foot. 

If the model is to be a Bleriot, then as the original 
has a span of 28 ft., the model may be built to a scale 





MODEL AEROPLANE FUSELAGES 33 


of 1 in. to the foot. The Wright machine has a span 
of 41 ft., so a model to § in. to the foot would have a 
span of 30§ in. In this case, perhaps, 1-in. scale 
would not be considered too large. Odd scales such as 
J in. to the foot can, of course, be adopted; but what¬ 
ever the scale is to be, the model should be set out 
full size on a sheet of cartridge paper, and the scale 
drawn accurately at the foot. The ribs should be 
built up as in Fig. 36. 

In designing a rubber-driven model, absolute scale 
must of necessity be departed from, except in the prin¬ 
cipal measurements and in the distance of centres 
apart of spars and other important members, which if 
not reproduced in their proper form and position would 
mar the otherwise correct appearance of the machine. 
Many of the spars will, of course, need to be increased 
in cross-sectional dimension in order to make them of 
sufficient strength. Borne efficient wing plans are 
given by Fig. 37. 

Stated briefly, there are essentially three kinds of 
model aeroplanes. First, the scale model, which is a 
reproduction to scale of a real machine ; second, a modi¬ 
fied copy of a large machine, which is so designed as 
to resemble in general form some well-known proto¬ 
type, while retaining by means of a suitable motor, 
generally twisted rubber, some ability to fly; third, 
a machine which does not in any way follow the 
lines of full-size machines, and is built for flight 
only. 

The first of these is essentially an exhibition model; 
it is more often built either to illustrate points in 



34 


MODEL AEROPLANES 


the design and construction of large machines, or to 
demonstrate the functions of the various parts to 
technical classes, etc. 

Scale models, as a rule, are unsatisfactory flyers, 
and if they fly at all the flight is so short that little can 
be learned from their performance. 

Some serviceable types of bearings are given by 
Figs. 38 and 38 a, on p. 31. 



CHAPTEB IY 


Practical Construction: Carving Air-screws 

One of the most important units of an aeroplane, 
whether full size or model, is the screw, since excel¬ 
lence of design with regard to the other portions of 
the machine are rendered void if the means of 
converting the power of the engine into work are 
inefficient. 

The action of an air-screw may be likened to a 
bolt turning in a nut (the screw being the bolt and 
the air the nut), the difference being that whereas 
one turn of a bolt with, say, a Whitworth pitch of 
14 threads per inch in a nut is bound to advance a 
distance equal to the pitch = ^ in., an air-screw may 
only advance 75 per cent, of its theoretical pitch, owing 
to the yielding nature of the air. This loss in efficiency 
is called “slip,” and is usually expressed as a percent¬ 
age of the theoretical pitch. Thus a screw with a 
theoretical pitch of 4 ft., which possesses 75 per cent, 
efficiency, has an effective pitch of 3 ft. That is to 
say, each turn of the screw will take the aeroplane 
forward 3 ft. If, however, the screw were working 
in a solid, it would advance its theoretical pitch 
= 4 ft. A greater efficiency is obtainable with screws 
working in water, owing to the difference in density 
of the two media, namely, air is to water as 800 : 1. 

35 


36 


MODEL AEROPLANES 


Probably no air-screw has yet exceeded 80 per cent, 
efficienc}^ 70 per cent, being a fair average. 

It may, perhaps, not be amiss to outline some of 
the factors involved in the design of an air-screw. 
Having decided on the diameter of it, the proportions 
of the block from which the screw is to be carved are 
required. It is a very good rule to make the pitch 
from one and a half to twice the diameter for single¬ 
screw machines, and from two and a half to three 
times the diameter for twin-screw machines. It is 
possible to use much longer-pitched screws with twin- 
screw machines (it being understood that the screws 
revolve in opposite directions), since the torque, or 
tendency of the screw to capsize the machine in the op¬ 
posite direction to which it revolves, will be balanced. 
For the purposes of this chapter, however, it is pre¬ 
supposed that a screw 7 is required for a single-screw 
machine, and a diameter of 12 in. has been 
decided on. One and a half times 12 in. gives 
18 in. as the pitch. Remembering the formula for 

thickness of block 

pitch, P = 3y x D x T 7 ~ — 7 ~;—, where 

r . width of block 

P = pitch, D = diameter of screw, and using a 

ratio of width of blade to diameter of screw of 

6 : 1 (which gives 2 in. as the width of block) 

22 12 thickness of block 

x --x --- 

7 1 2 


gives 18 = 


, from 


which thickness of block = *954 = 


61 

64 


approx. 


The block may now be prepared from these dimen¬ 
sions. American whitewood, silver spruce, mahogany, 






Figs. 39 to 48.—Carving Air-screws. 

















38 


MODEL AEROPLANES 


or walnut are the most suitable woods to use. The 
block should be planed up true and square, and a hole 
drilled axially through its geometrical centre. The 
first operation is to rough the block out to the shape 
shown by Fig. 39, which shows the Chauviere type. 
Of course, other shapes may be used as desired, but 
the method of manufacture is the same. Now, with 
a flat chisel or woodworker’s knife pare the wood away 
(see Fig. 40) until the hollow or concave side of the 
blade is formed (see Fig. 41). The obverse side of 
the other blade is then similarly treated (see Fig. 42), 
which clearly shows how the blade is hollowed out. 

Fig. 43 shows the method of forming the boss of 
the screw, and Fig. 44 how the reverse or convex side 
of the blade is shaped. Fig. 45 shows the screw 
roughed out, and Fig. 46 indicates the glass-papering 
operation. 

At this stage the screw has to be balanced. This 
is of great importance, since the screw that is un¬ 
balanced loses a great amount of efficiency owing to 
the consequent vibration when it rotates. In full-size 
practice it would be highly dangerous to use a screw 
that is not balanced. 

A piece of wire is passed through the hole 
previously drilled, and the heavier blade carefully 
glasspapered down (with No. 00 glasspaper to finish) 
until the screw poises in a horizontal plane. Fig. 47 
shows the sort of brush to use for polishing, and 
Fig. 48 the finished screw. 

For models that require a good finish an excellent 
form of construction (incidentally it may be remarked 



CARVING AIR-SCREWS 


39 


that fall-size screws are made in this way) is that 
shown by Fig. 49, the laminated type. These 
laminated screws are exceedingly strong, as the 
grain, by virtue of the splayed blanks, follows 
the blade. Screws carved from the solid block are 
a trifle weak near the boss owing to cross grain. The 



laminae could be alternate layers of whitewood and 
mahogany, which give a pleasing finish to the screw. 
A is an end view of a carved screw. 

The method of obtaining the pitch angles at 
various points along a screw-blade is shown diagram- 
matically in Fig. 50. It will be obvious that the pitch 
of a screw should be constant along the whole length 
of blade, so that the air is deflected or driven back 

















40 


MODEL AEROPLANES 


at a constant velocity. An efficient screw will deliver 
a solid cylinder of air, whereas an inefficient one 
delivers a tube of air. 

If, for instance, the pitch at the propeller tip is 
30 in., whilst at, say, 3 in. from the centre it is only 
25 in., obviously the tip of the screw will be imparting 



a higher velocity to the air than the portion approach¬ 
ing the boss, and thus this latter would be acting as 
a drag upon the other portion. 

The method is to lay off a distance, equal to the 
pitch, to some convenient scale, and to erect another 
line vertically and to the same scale equivalent to the 
circumference of the disc swept by the propeller, which 
may be called the peripheral line. Subdividing this 
line into a convenient number of equidistant parts 
(three or four are sufficient for screws up to 14 in. in 
diameter), and connecting up the points so obtained 






















CARVING AIRSCREWS 


4 i 


to the right-hand end of the base line, gives the pitch 
angles at the corresponding points of the blade. It is 
the subtended angles which are required, as indicated 
by the arrows. 

Templates should be cut to these angles (which, 
of course, are the angles made with the axis) with 
which to check the angles along the blade during 
construction. This checking is more necessary with 
bentwood screws than with carved ones. 



CHAPTER V 


Practical Construction : Bending Air-screws 

* 

Great diversity of practice exists with regard to the 
construction of model air-screws, some aeromodellists 
favouring small diameter with long pitch, others long 
diameter and short pitch, and still others who adhere 
to either bentwood or carved screws in either of the 
above forms. Generally speaking, a screw with a large 
diameter in proportion to short span has a short pitch, 
say one and a quarter times the diameter, while those 
having a short diameter in relation to span should have 
a fairly long pitch, from one and a half to twice the 
diameter. It is a useful rule to make the diameter 
approximately one-third the span of the machine for 
either single-screw or twin-screw machines. This 
relation seems to give a very small effect on lateral 
stability, whereas when the diameter is made larger, 
the machine has a tendency to capsize laterally in the 
opposite direction to which the screw revolves. This 
force is known as torque. 

It can, however, be fairly claimed that, for a given 
torque or turning power, better results are usually 
obtained with carved screws, whether short or large 
ones are used. The writer personally prefers a large- 
diameter and short-pitched screw, because, as the 
sciev* tlnust is equal to the weight of air displaced, 

42 






Figs. 52 and 53.—Standard Types of Bentwood Screws 













































44 


MODEL AEROPLANES 


the larger the screw the greater is the proportion of 
air driven back in proportion to diameter. That is to 
say, double the diameter and four times the volume of 
air is displaced for only a double expenditure of power. 

It is difficult to speak positively on the question of 
the best speed at which a screw should rotate, as the 
loading per square foot of surface enters into the 
proposition. If a model has 1 sq. ft. of surface for 
every ounce of its weight, there is a speed at which 
the main surface will give a maximum of lift for a 
minimum of power, and a screw must be fitted whose 
pitch, multiplied by its revolutions per minute, equals 
the distance per minute the model should fly. If a 
screw that is too fast is fitted the model will show a 
tendency to “stall/ 5 or ascend nose first, and if too 
slow a one is used the model will appear to be under¬ 
powered. 

The writer has outlined these points to emphasise 
the fact that no definite rules, but only approximations, 
can be laid down, owing to the large number of un¬ 
known quantities which would have to be taken into 
consideration. As the aero-modellist, however, be¬ 
comes accustomed to puzzling out the many little 
problems connected with model aeroplaning, he 
speedily diagnoses the complaint of a refractory 
machine, and applies a remedy accordingly. 

The accompanying illustrations (see page 43) show 
the method of making bentwood and screws. Fig. 5] 
is a view of a finished pair of propellers. To the left 
of this illustration is given the method of setting out 
the blank in terms of pitch and diameter relations. 



BENDING AIR-SCREWS 


45 


The maximum blade width should be located one-third 
of the radius from the screw tip, and should be about 
one-eighth the diameter. This latter, in turn, should 



Tin 5t'np 


Fig. 54. — Bentwood 
Shaft Attachment 




be two-thirds of the pitch. Inversely, therefore, the 
pitch should be one and a half times the diametei. 
With twin-screw machines this may be extended to 


D 









































46 


MODEL AEROPLANES 


twice the diameter, or even more, but should never 
exceed three times the diameter. 

Fig. 52 is a view of the Camm type of bentwood 
screw, which has a high thrust to power ratio. Birch 
should be used for bentwood screws, as this bends 
easily and yet has a tenacity which is lacking in other 
woods. Ash or hickory may be used as an alternative, 
but neither of these is as satisfactory as birch. Before 
bending, the blanks should be filled with gold size to 
keep the blade as rigid as possible, and prevent it from 
going back or flattening out after bending. 

Fig. 53 shows the Twining type of screw, which 
has long, narrow tapering blades and fine pitch. Under 
test this has given extremely satisfactory results, and 
can be recommended. 

Fig. 54 shows the method of attaching spindles 
to bentwood screws, a strap of tin being wrapped round 
the blank centre to which the shaft is soldered. Care 
should be taken to ensure that the shaft is quite central 
sectionally and diametrically. 

A method of securing carved-screw shafts is shown 
by Fig. 55, and is self-explanatory. When the elastic 
skein is in tension it has a tendency to pull the hooks 
out straight, so releasing the skein, with sometimes 
painful consequences to the hand. The safety hook 
shown by Fig. 56 has a brass-tube collar which slides 
over the end. All the hooks should be covered with 
valve tubing, to prevent the elastic cutting through. 

Fig. 57 gives the proportions of the Camm bent¬ 
wood blank, and will require no explanation beyond 
the fact that it is bent along the dotted lines. 



CHAPTER VI 


Practical Construction : Planes 

There is little difference of opinion regarding the 
construction of the planes of a model aeroplane, and 
the methods of making can be classified under three 
headings—cane, wood, and wire. 

There are advocates for each form of construction, 
and it is difficult to state definitely which is the best 
practice, each having equally good results. The wire 
plane, especially when steel wire of the music or piano 
variety is used, is much stronger, offers less resistance 
to the air, and has a neater appearance than the others, 
but it is slightly the heavier. A wooden plane can 
also be made extremely neat and light, although it 
is a little weak. Birch is the best wood to use for 
this purpose, as it is extremely tough and not too 
heavy. Where cane is used for the frame, pinning 
and gluing is out of the question, hence binding and 
gluing must be resorted to. A plane so made is very 
strong and flexible, and will withstand a great amount 
of rough usage. It is, however, not neat in appear¬ 
ance and hardly to be recommended, although many 
prizes have been won by models possessing such 
planes. 

Yet another form which can be considered good 
practice consists of a combination of umbrella ribbing 

47 


48 


MODEL AEROPLANES 


and piano wire. This gives a very rigid and almost 
unbreakable plane, but its weight for small machines 
is prohibitive. It should chiefly be used for power- 
driven machines, power in this instance meaning any 
form of motive power other than elastic. 

The Wooden Plane. —In constructing wooden 
planes it is usual to adopt the method shown by 
Fig. 58. The spars are set out to their correct 
positions but left overlapping, so that the pinning 
operation does not split the ends out. The pins should 

2 


daaty^isofJoint' onA 

Fig. 58.—Wooden Planes 

be driven through to secure the frame to bench, so 
that it remains true until the glue has set. Whereupon 
it may be prised up with a pocket-knife, and the pins 
clinched over as shown in the joint analysis A. The 
centre rib should be trimmed up as shown at B, to 
piovide a means of attachment of the completed plane 
to the fuselage or body of the machine. Two spars 
are sufficient for models up to 36-in. span, but over 
that three spars should be used, as in the part plan 










< 









\ 




























PLANES 


49 


(Fig. 59), or two spars spaced closer together, as in 
Fig. 60, may be used, with a thread trailing edge. 



This gives a neat appearance to the finished plane 
and greater rigidity. 


























































































5o 


MODEL AEROPLANES 


The Cane Plane. —Another form of construction 
that is very light is that shown by Fig. 61. Here a 
length of thin cane is bent to the form of the outline, 
the ribs being bent to align with the leading and 
trailing edges. Gluing and binding is used here. 
Such a plane can be made light, but it always has an 
appearance anything but neat. It cannot be advocated 
for machines over 30 in. in span. 

The Umbrella-ribbing' Plane. —Umbrella ribbing 
can be utilised, in conjunction with piano wire, for 
plane construction as shown by Fig. 62. The channel 
of the ribbing should be thoroughly cleaned with emery 
cloth, so that the leading ends of the ribs can be 
soldered therein. Three spars should be used for spans 
over 30 in. 

For the planes of model flying machines steel wire 
offers exceptional advantages, as it is practically un¬ 
breakable and can be bent to any desired shape. 
Another advantage is that it offers a minimum resist¬ 
ance when travelling in the air. To the uninitiated, 
the making of steel-wire planes is a difficult under¬ 
taking ; but if the following instructions are carefully 
carried out the planes will prove very satisfactory. 

First procure a piece of wood about J in. thick 
and slightly larger than the plane to be made, and 
draw on it a plan of the plane as shown in Fig. 63. 
For example, it will be assumed that a plane 30 in. 
span and 5 in. wide, having four ribs, is to be made. 
For planes approximately this size, No. 17 s.w.g steel 
wire is employed. Before beginning the work the 
wire should be straightened as much as possible. Then 



PLANES 


5i 


lay the wire over the plan, beginning at a (Fig. 63) 
and passing round to b. As the wire is bent to the 
shape of the plan, it must be fastened down to the 
board by means of small staples. Then cut four pieces 
of wire for the ribs c, d, e, and f, allowing J in. each 
end for turning at right angles as in Fig. 63. 

The framework is now ready for soldering together. 
It is essential that the wire and soldering bit must 
be perfectly clean. Apply a little killed spirits of salt 



Figs. 63 and 64,—Making Wire Planes 


to the parts to be soldered, and then place a piece of 
solder in position and touch with the hot soldering bit. 
Care must be taken to see that the wires lie close 
together. 

When the plane is soldered together remove all the 
staples and clean up all the joints with a file. The joints 
must now be bound round tightly with fine iron wire, 
























52 


MODEL AEROPLANES 


which must be perfectly clean. The plane must now 
be fastened to the board again, and all joints soldered 
When the soldering is completed the plane 

is once more re¬ 
moved from the 


again 



board, straight¬ 
ened* the dihedral 
angle given, and 
the ribs bent to 
the desired cam¬ 
ber. If the sol¬ 
dering has been 
carefully accom¬ 
plished there is no 
fear of the joints 
giving way. 

For covering 
planes it is far 
better to purchase 
a waterproof silk 
especially manu¬ 
factured for the 
purpose than to 
attempt to use 
ordinary silk. 
The silk varies 
in weight from 
1 oz. to 1J oz. 

per square yard. When cutting the silk about J in. 
must be allowed for turning over for fastening. At the 
curved ends of the plane slits about J in. apart must be 


>©*) 

c 


o 

« 

M 


a 

v 

£ 

CD 


ir, 

VO 


•ot) 

£ 
























































PLANES 


53 


cut in the edge of the silk, as shown in Fig. 64. Apply 
a thin coating of glue to the silk (use seccotine) to 
be turned back, and allow sufficient time for the glue 
to get tacky. Then stick over the plane, beginning 
at A (Fig. 64) and finishing at B. Allow time for the 
glue to set, then fasten the opposite end in the same 
manner. Care must be taken to stretch the silk 
tightly, so that it is free from wrinkles. Then fasten 
first one side of the plane and lastly the other. 

Another method of covering steel-wire planes is to 
lace the silk to the framework. The silk must be cut 
about J in. larger than the framework, and the edges 
hemmed with a sewing machine. The silk cover when 
hemmed should be slightly smaller than the frame¬ 
work. First sew the silk roughly in position, and then 
carefully sew it, beginning at one end, following with 
the other end, and lastly the sides. The stitches should 
first be passed through the silk, and then round the 
wire at intervals of about \ in. 

Fig. 65 is the plan of a swept-back wire plane. 

The plan should be drawn full size on a board by 

* 

means of squares, the contour of the plane being 
contiguous in relation to the squares as that in the 
illustration and the method outlined above followed. 
The ribs should also be fitted up to the outline, being 
bound and soldered to the piano-wire frame. For 
machines above 30-in. span a third strengthening spar 
should be fixed in the position of the dotted line to 
obtain rigidity. Two central ribs should be fitted to 
provide a spar-attachment. The tips require to be set 
at a slight negative angle as at c. 



CHAPTER YII 


Simple Twin-Screw Monoplane 

The accompanying illustrations show as simple a type 
of model aeroplane as it is well possible to make, 
excluding the now obsolete single-stick hand-launched 
1—1—PI. It is thus a suitable model for beginners, 
flights of well over a quarter of a mile being easily 
obtainable. 

The main spar (see Fig. 66) is cut from straight¬ 
grained birch, to the dimensions given, each end of 
it being tapered down to -ft- in. square. The propeller 
bar is of silver spruce, § in. by J in. in cross section. 
The end of the main spar is slotted to receive the 
propeller bar, this latter being pinned and glued into 
position. The propeller-bar support is similarly slotted 
to take the bar, a pin being driven through the two 
and clinched over on the under-side. Fig. 67 clearly 
shows both joints. At 6 in. from one end the main spar 
is mortised to receive two tenons which are cut on the 
ends of the bar supports. These tenons should be so 
cut that they butt to one another in the centre of the 
mortise. An idea of the shape of the tenon will be 
gathered from Fig. 68, a view of the joint assembled 
being given. 

Two brass propeller bearings will now be required. 
They should be cut from No. 20 gauge brass, a hole 
being drilled in each to allow the No. 18 gauge 

54 


















































5b 


MODEL AEROPLANES 


propeller shafts to rotate freely. Each bearing is 
bound on with three-cord carpet thread, a portion of 
each being left overhanging the bar to provide clear¬ 
ance for the revolution of the shaft. These projections 
should be bent at an angle of 90° to the skeins of 
rubber, so that the bearing faces present true surfaces 
for the screws to revolve on. Details of the bearings 
are given by Fig. 69. Two hooks bent from one 
continuous length of wire are bound to the nose of 
the machine, to embrace the skeins of rubber. All 
bindings on the machine should be smeared with weak 
glue. 

In Fig. 70 details are given of the spar bracing 
outrigger. The binding, for the sake of clearness, is 
omitted. A piece of wire (hard-drawn brass is suited 
to the purpose) is passed through the spar, a portion 
being bent to align with each side of this. It is then 
bent outwards, the ends being pulled round a piece 
of No. 20 gauge wire secured in the vice, to form eyes, 
through which the bracing passes. The outrigger arm 
is 2 in. long, the cranked portion of it being bound 
to the spar. The bracing is attached to small No. 
20 s.w.G. hooks bound to each end of the spar at 
the points shown. Care should be taken to apply 
equal tension on each wire, or the spar will become 
warped. 

The elevator is built from No. 18 s.w.G. piano 
wire. All joints are bound with fine wire and soldered. 
The centre rib continues over the leading edge, being 
bent downwards and backwards as at A (Fig. 66). This 
projection fits into a hole drilled in the nose of the 



SIMPLE TWIN-SCREW MONOPLANE 57 


model; and, being bent at an angle, the trailing edge 
binds on the spar with sufficient friction to retain it 




Fig. 73.—Elevation of Main Plane 




Fig. 72-Detail 

of Plane Bracing 


in place, but yet permitting it to swivel should it strike 
any object when flying. 







































58 


MODEL AEROPLANES 


The main planes are built from birch J in. by t 3 ^ in. 
in cross section, the trailing spar being bent in a jet 
of steam, so that its ends sweep forward, as shown in 
the plan view. The ribs are pinned and glued to the 
spars, the pins being clinched on the under-side. The 
centre rib is left overhanging the spars, as shown in 
Fig. (71), to enable the tin straps (lapped and soldered 
together as at a) to slide over them and secure the 
wing to the spar. A section of the joint is given by B. 
By removing these straps it is thus possible to alter 
the disposition of the main surface, when it is desired 
to adjust the elevation of the complete model. Fig. 71 
is a perspective view of the centre rib, the strap being 
shown black. To move the main plane each clip is 
forced off the extensions of the centre rib and thus 
releases the wing. Each clip is cut from tinfoil to 
the dimensions given at A (Fig. 71), being bent to a 
rectangular shape, and soldered up. b is a section of 
the joint. Fig. 72 indicates the method of attaching 
the diagonal wing bracing, which imparts a dihedral 
angle of 1-J in. to the plane. A lj-in. dihedral means 
that each wing tip is 1J in. above the level of the spar. 
An elevation of the main plane is given by Fig. 73. 

Two propellers, of right-handed and left-handed 
pitch (for the reason, see p. 36)., must be bent from 
birchwood 12 in. dia. x 1J in. wide, by in. thick; 
a finished view of the two screws is given by Fig. 74. 
For more comprehensive details of air-screw construc¬ 
tion see chapters IY and V. 

Some details are also given of a similar design, the 
difference being that the former machine is built for 




Figs. 75 to 77.— Another Simple Monoplane Design 





















































6o 


MODEL AEROPLANES 


distance, whilst the latter (see Fig. 75) is built for 
duration. The main spar is of spruce § in. x J in. 
in cross section and of the length shown in Fig. 75. 
The main plane, as with the previous machine dealt 



Fig. 78.—Finished Model 


with, is adjusted by means of the tin clips and 
extending centre-rib; a plan of the outrigger is also 
given in Fig. 76. The main plane has a dihedral angle 
of 1J in. A is a side elevation of the elevator, showing 
its angle of incidence in relation to the spar, and 
Fig. 77 a perspective sketch of the elevator. An idea 
of a model of this type flying can be gathered from 
Fig. 78. 





CHAPTEE VIII 


Simple Twin-screw Biplane 

AccoPiDTNG to the type formula, the machine illustrated 
on p. G3 is of the l-2-p2 type, which signifies that 
it has two superposed main supporting surfaces and 
twin screws, and that it flies with the small plane 
leading. The writer, in testing the model from which 
the drawings were made, found that 300 yards were 
easily obtainable at every flight at an altitude of 40 ft. 
or so. Although its construction is slightly more 
complicated than a monoplane, this is amply com¬ 
pensated for by its majestic appearance in the air. 

The central spar is hollow, and measures 36 in. by 
f in. by -fa in. Eig. 79 shows a cross section of it. 
Spruce was used for this, a groove J- in. by A in. 
being ploughed in the spruce, and a A-in. strip being 
glued over the open side. The spar should be tapered 
off from a point 12 in. from the front end to J in. by 
J in., to give additional strength. 

The propeller bar is mortised into one end of the 
central spar, and is stayed from a point 6 in. from the 
rear end to J in. in from each end of the propeller bar, 
to which projection the bearings, cut from sheet brass, 
are lashed. These latter are shown in Fig. 80. Tc 
the front of the spar are bound two hooks, formed 
from one continuous length of wire. These embrace 


62 


MODEL AEROPLANES 


the rubber, and should be covered with valve 
tubing. 

Pour birch struts should next be cut, J in. by -fa in. 
in section and 7 in. long, to support the main aerofoils 
on the spar. They should fit over the spar in the 
position shown, small blocks uniting them top and 
bottom, and should be so fixed that their upper ends 
are 3 in. off the spar. Notches are to be cut in them 
2J in. below the spar, to form a convenient fixing for 
the lower main plane. Pig. 81 clearly shows the struts 
united to one of the blocks; the saw cuts or notches 
will also be apparent from this. 

A cane skid is bound to the lower blocks, and to the 
spar at the position indicated in Pig. 82. A half-section 
of a round cane is quite suitable for this purpose. 

A plan view of the model is given by Pig. 83, from 
which the relative position of ribs, planes, etc., will 
be seen. Pig. 84 is an end elevation looking through 
from the propeller end. It will he observed that the 
screws rotate from approximately the centre of 
resistance. The measurements given should be care- 
fully followed to see that this is so in the completed 
model. The dihedral angle of the planes should be 
made 1J in., which is ample to provide lateral stability,. 
Longitudinal stability is provided by an angle of 
incidence on the elevator (Pig. 85). 

The elevator is constructed from one continuous 
length of No. 18 gauge piano wire. It is rectangular 
in plan, the joint being a soldered one at the centre 
of the trailing edge. The centre rib projects down¬ 
wards for 1J in., which projection fits into a hole bored 




Figs. 79 to 85.—General Arrangement and Details of Biplane 























































































64 


MODEL AEROPLANES 




in the nose of the machine with just sufficient friction 
to retain it in place. It should also be bent back at 
an angle to cause the trailing edge to bind on the spar 
sufficiently to allow it to swivel in the event of it 
striking any fixed object. From this centre rib the 
elevation of the complete machine is adjusted. The 
main planes are constructed from birch \ in. by to in, 
in cross section, five ribs connecting the longer spars. 
No camber is given to the ribs; they should be cut 
off 1 in. or no longer than is necessary, pinned to the 
spars, so that the latter are 5 in. apart, and cut off 
flush after the glue is dry. The top plane, it will be 
noticed, has an overhang of 3 in. The planes are 
covered underneath to eliminate the undulations which 
would otherwise be caused by the ribs. Fabric should 
be sewn to the elevator frame. 

The top plane is lashed to the struts in the manner 
shown in Fig. 86, the centre rib resting on the small 
wooden blocks, while the bottom plane is sprung into 
the notches previously referred to. Four No. 20 s.w.g, 
wire stanchions, with eyes bent in them top and 
bottom, as shown in Fig. 87, will next be required 
to form an anchorage for the wing bracing, and to 
maintain the “gap ” at the tips of the wings. Brass 
wire will do for them, and when made their ends 
should be forced through the spars in the position 
shown in the end elevation, and then clinched over. 

Bracing the wings should next be undertaken, and 
carpet tlnead should be requisitioned for this purpose 
It is the easiest matter possible to warp the wings in 
this operation, so that too much care cannot be taken 



SIMPLE TWIN-SCREW BIPLANE 65 


in this respect. It should be understood that the 
bracing is fixed to holes in the wooden stanchions, 
where it must be securely tied, and not continued to 
the opposite side without, or the wings will rock later¬ 
ally, and so cause instability. Sufficient tension should 
be placed on the threads which pass to the wing tips of 
the bottom plane to impart a lj-in. dihedral angle. 

The last, and perhaps the most important, unit of 
the model should be made—the propellers. Cut a 



Fig. 87 



pair of blanks, as shown in Fig. 88, to shape from 
3 ^-in.'birch to form the propellers. Strips of tinfoil 
are wrapped round their centres, to which the spindles 
are soldered. Bend the blades at the dotted lines under 
a jet of steam from a kettle, making them to revolve 
in opposite directions. They rotate on steel-cupped 
washers placed on the spindles. 

Motive power is supplied from eight strands per 
side of J-in. strip rubber well lubricated with soft soap 
emulsified with water. These skeins will stand 650 
turns each, which number should be gradually worked 
up to on new rubber, and not applied at the first flight. 
A perspective view of the finished model is given in 
Fig. 89, 







66 


MODEL AEROPLANES 


Flying the Model, —Having selected a large open 
space clear of trees, give about 100 turns on the pro¬ 
pellers in order to adjust the elevator. If the model 
points its nose in the air it is elevated too much. If 
the model flies too low it is not elevated enough. In 
each case it requires adjustment untd the precise 
position is arrived at. The elevator should never be 
at a greater angle than 8° or less than 5°. If the 
machine still flies too low with the elevator at 5° the 
main planes will have to be moved forward slightly; 



but the exact position is only found by experiment. 
If it flies too high with the elevator at 5° the planes 
will have to be put back. 

Much depends on the way a model is launched. 
The proper way is to hold it by the propellers, with 
the thumb and forefinger along the main sticks, taking 
care not to bend the propeller hooks; then hold at 
about the angle shown in the photograph (Pig. 90), 
and launch as near as possible with the wind. 





SIMPLE TWIN-SCREW BIPLANE 0; 


It is necessary when flying in windy weather to 
launch the machine high and smartly, as the wind 
has a tendency to beat it to the ground. Both pro¬ 
pellers must be released at exactly the same time. It 


r* 



Fig. 90.—Launching the Model 


should be carefully watched while it is flying, and if 
it persists in turning, say to the right, the fault will 
probably be that the left propeller is more effective, 
or the planes on the left side of the machine are 
elevated more. For straight flights it is most 
important that all the planes should be in perfect 
alignment; but to succeed in making a twin-propelled 




r * 


MODEL AEROPLANES 


bS 


model fly perfectly straight is largely a matter of 

( * 

perfect construction. 

The model can be steered by means of the elevator 
(looking at the machine from the propeller end); if 
the elevator is lowered on the left side it will fly round 
to the left, and vice versa. The adjustment necessary 
to effect this can be accomplished by means of the slot 
in one of the elevator uprights. 



CH APT Ell IX 


Winders for Elastic Motors 

To a model aeroplane enthusiast a. winder is an 
enormous acquisition. The converted egg-beater type 
of winder, so much in evidence, leaves much to be 
desired, the chief fault being that the bearing spindles 
wear so quickly, apart from the fact that they are 
awkward to manipulate single-handed. A second 
person is generally required to support the model. 

The winder here illustrated bears the distinct 
advantage that one person can wind, keep the model 
in alignment with, and forced into, the chuck 
simultaneously. The construction and general details 
will bo fairly obvious from the accompanying illustra¬ 
tions, so that it will only be necessary to give a brief 
description. 

It consists of an ash stump, 13 in. by 1 in. by 1 in., 
tapered at one end, as in Fig. 91, to facilitate its being 
forced into the ground. A gear and pinion (see 
Fig. 91), which may be requisitioned from some of 
the cheaper type of clockworks, are mounted at the 
top end of the stump in a casting of Xo. 18 s.w.G. 
brass, which is secured to the ash bv means of two 
round-headed screws (see Fig. 94). It will be found 
that for general purposes a gear ratio of six to one will 

be most suitable. Thus the pinion may have ten teeth 

6 9 


70 


MODEL AEROPLANES 


and the gear sixty. The handle should be bent to 
shape after being passed through the stump. Copper 
ferrules are used on the spindles to keep the gears 
central between the casing, as shown in Tig- 93, and 
should allow a little play to ensure easy rotation. The 



Figs. 91 to 94.—A Model Aeroplane Winder 


pinion spindle must be flattened out after the gearing 
is put together, and the hardwood chuck then driven 
on. A glance at Fig. 92 will show clearly what is 
meant. The slot in the chuck should be made 
sufficiently large to take a carved propeller. 

A Double Winder. —As each propeller of a twdn- 
screw machine requires to be wound up 400 to 500 
times, it is obviously necessary to use a geared-up 









































Fig. 95a.—Using Twin Winder * 














72 


MODEL AEROPLANES 


winder. This can easily be constructed out of an 
ordinary egg-beater, and one converted into a very 
useful instrument is shown by Fig. 94a. The great 
advantage of using a winder of this type is that both 
propellers can be wound simultaneously. Figs. 95 
and 95a clearly show how the alteration is made; it is 
quite simple, and all the tools required are a three- 
cornered file, a drill, and a soldering bit. The egg- 
beater can be obtained for a few pence at any iron¬ 
monger’s. The two hooks at the nose of the machine 
are attached to the cross-pieces on the winder, and 
the rubber is wound in the same direction as the pro¬ 
pellers revolve (see Fig. 95a). The winder shown is 
geared 5 to 1, so that 100 turns on the winder gives 
500 turns on the propellers. Geared-up winders may 
be purchased fairly cheap. 



CHAPTER X 


Collapsible Monoplane 

The difficulty of carrying a fairly large model to a 
convenient Hying ground prevents many would-be 
makers taking a ’ practical interest in model flying. 
The necessity of overcoming this difficulty has resulted 
in several excellent designs, one of the best being 
the monoplane designed and constructed by Mr. A. B, 
Clark, the secretary of the South-Eastern Model Aero 
Club. When this model monoplane was built the 
objects aimed at were extreme reliability and easy 
conveyance to and from the, flying grounds situated 
some distance away. 

The model is fitted with a chassis to enable it to 
start off good ground under its own power; but this 
starting-gear is so constructed that the whole model 
will pack up flat and make a convenient parcel. In 
fact, the complete model will easily go into a cardboard 
box measuring 2 ft. 10 in. by 1 ft. 2 in. 

Referring to the accompanying illustrations, 
Fig. 9G shows the plan view of the complete machine, 
Fig. 97 a side view, and Fig. 98 a front view. The 
body (fuselage) is made of two' pieces of silver spruco, 
3 ft. G in. long, § in. deep, and ft- in. thick. These 
gradually taper towards each end, where they measure 
J in. by ft in. Two distance pieces of bamboo are 

73 


74 


MODEL AEROPLANES 


shaped to streamline form and placed at equal distances 
along the fuselage; the front piece is 2f in., the otliej 
2 in. These pieces should be pointed at the ends, and 
fit in a slot made in the side lengths, as indicated at A 
(Fig. 99), and then bound very tightly with glued 
narrow silk tape or ribbon, as indicated at B. This is 
the neatest and also the strongest method of making 
joints for model aeroplane frames. The ends of the 
two long lengths should be bound together with strong 
thread and carefully glued. 

The tail (used in place of the familiar elevator) is 
built on to the rear end of the fuselage, and is com 
posed of two pieces of yellow bamboo, 9J in. by A in 
by J in., tapering to J in. square at the end to which 
the propeller bearings are attached. These bearings 
are made of No. 18 or No. 20 s.w.G. piano wire, and 
their shape is clearly shown in Fig. 100. The 
bearings are bound to the inner edge of the wood with 
glued thread or fine flower wire. The wide ends of 
the bamboo lengths are held over a bunsen (the blue 
flame of an incandescent burner is very suitable), and 
bent to the angle shown in Fig. 96. The trailing edge 
of the tail is made of No. 26 s.w.G. piano wire, or a 
G banjo string. The wire is taken right through the 
end of the fuselage, a small hole being carefully drilled 
J in. from the end. A bead of solder should be run 
on the wire on both sides of the hole, to prevent move¬ 
ment in a lateral direction, and the two ends are taken 
through the bearings and bound to the bamboo with 
fine wire, leaving sufficient to form hooks for the two 
bracing wires to be afterwards attached. The whole 




Figs. 9) to 101.—Arrangement and Details of Collapsible Monoplane 



























76 


MODEL AEROPLANES 


of this tail framework is covered with proofed silk 
on both sides, thus forming an approximate streamline 
surface, which has proved remarkably efficient. Two 
triangular pieces of silk should be cut out, just large 
enough to give sufficient overlap. They should be 
attached with fish glue, and stretched as tightly as 
possible. 

\ 

At the other end of the fuselage is attached the 
hooks for the elastic, and the wire forming them is 
also utilised as a protector. The whole construction 
is made from a lOJ-in. length of No. 18 s.w.G. piano 
wire, reinforced with a strip of thin bamboo, bent to 
shape over a blue dame and bound with silk tape. The 
part is shown unbound in Fig. 101, and Fig. 102 shows 
an alternative protector; but it is not so effective. 

The main plane is made of bamboo and piano wire 
of No. 18 s.w.G., and measures 2 ft. 10 in. by 6J in. 
The leading edge is of bamboo 3 ft. 2 in. long, xg' in. 
wide, tapering to 1 in. at the ends, with a uniform 
thickness of J in. When planed down the length 
should be heated over a blue flame, and bent to the 
shape shown in Fig. 96, the outside of the bamboo 
being kept on the outside of the curve. The trailing 
‘edge should now be attached to the ends of the leading 
edge, a length of \ in. being bent up at each end of 
the wire, and securely bound to the bamboo. The ribs 
:Should now be cut from the same gauge wire. The 
lends should be bent out at an angle so that they may 
be bound to the leading and trailing edges., as shown 
Sin Fig. 103; the projecting ends should be about § in. 

The two centre ribs are shaped as shown in Fig. 





Fi£s. 102 to 109. Details of Collapsible Monoplane 


Fig. 105 


F 































MODEL AEROPLANES 



104. It will be seen that the leading edge is raised 
J in. above the fuselage, and the rear edge is level with 
it. The ends of the ribs are fitted into small holes 
drilled in the top of the fuselage, and kept in position 
by means of small metal clips, as shown in Figs. 105 
and 10G. Four of the clips are required, and they 
may be easily made from thin tinplate and soldered. 





Hg. 110.—Rear Skid 



Figs. Ill and 112.—Details of Screw 


The ribs should be soldered to the trailing edge so as to 
make them secure. The framework should be covered 
with proofed silk, and neatly glued on all edges. 

The chassis is shown by Fig. 107, No. 18 gauge 
piano wire being used for the framing, and an ordinary- 
cycle spoke for the axle. Figs. 108 and 109 show the 
flexible joints of the chassis, which folds up flat when 
the hooks at c (Fig. 107) are withdrawn. 











COLLAPSIBLE MONOPLANE 


79 


The wheels are 2 in. in diameter, and are rubber 
tyred, the ends of the spoke being burred over to keep 
them in position. 

The rear skid is shown in Fig. 110, and is made 
of No. 18 gauge piano wire. A single length is used, 
being bent to shape, passed through the end of the 
fuselage, and held to its work by the projecting end d, 
which fits in a hole in the underside of one of the pieces 
of wood. When not in use the skid may be folded flat. 

The two propellers are of the simple bentwood 
type, 10 in. in diameter and 1 ft. 8 in. pitch. They 
are made of iV-in. birch in the usual way. The shape 
of the blades is shown in Fig. Ill, and the angle at 
which the blades are bent is shown in Fig. 112. Six 
strands of strip rubber should be attached to each 
propeller, ordinary soft soap being used as a lubricant. 



CHAPTER XT 


Tractor Monoplane 

Some of the competitions arranged by the Kite and 
Model Aeroplane Association have been for duration 
models of a minimum weight of 1 lb., capable of rising 
from the ground under their own power, carrying a 
dead weight of a quarter of their own total weight. 
Such a model is that here illustrated and described. It 
has flown repeatedly for thirty-eight seconds after 
rising from the ground, while its hand-launched dura¬ 
tion is about half a minute, by no means a small 
accomplishment for a lG-oz. model. It will be seen 
that it has somewhat larger dimensions than the 
ordinary rubber-driven model. 

The top main spar is of spruce, 4 ft. 6 in. long 
and J in. by J in. in cross section, the bottom one 
being 2 in. longer and J in. by -ft- in. in section. The 
bottom member is to be bent by steam approximately 
to the shape shown in the side view of the 
machine (Fig. 113), and then fitted to make a clean 
butt joint to the top spar b (Fig. 114). Bearings for 
the two f-in. gears, details of which are shown in 
Fig. 115, are bent to shape from No. 20 gauge sheet- 
brass, a lug being left projecting to engage with the 
bottom member of the fuselage. The holes for the 
shafts should be drilled so that the gears make a fairly 

8o 



Fig. 115.—Gearing Fig. 119.—Main Plane Attachment Fig. 118.—Chassis 















































82 


MODEL AEROPLANES 


tight mesh. The spindles are to be of No. 16 gauge 
piano wire, on to which the gears are to be soldered. 
The propeller shaft is continued forward of the bear¬ 
ing for 1J in., and is bent back at an angle (as shown 
in detail at a in Fig. 116) to grip tightly in the pro¬ 
peller boss. The gears are kept central between the 
two bearings by means of pieces of brass tubing, which 
are slipped on the spindles at each side of the bearing 
and soldered in position. 

Elastic hooks, formed from No. 16 gauge wire, are 
fixed at the rear end of the fuselage, and serve the 
double purpose of providing an anchorage for the bot¬ 
tom spar, which is whipped and glued with the hooks 
to the top spar. Eig. 114 shows clearly what is meant. 
Bamboo, of iV-in. by J-in. cross section, is used for 
the tail skid, which is secured to the fuselage by thread 
binding. Piano wire is used for the landing chassis, and 
of the same gauge as hitherto used on the spindles. 

The triangular side struts of the chassis should first 
be framed up from one continuous length of wire, lugs 
being bent at the point where they meet the fuselage, 
to be bound with fine tinned iron wire and soldered 
to the spar. Figs. 113, 117 and 118 clearly show its 
construction. Make the axle of such a length that a 
12-in. wheel-base may be left after the wheels are 
placed on. The writer found that 2-in. rubber-tyred 
disc wheels left nothing to be desired for rising off 
short grass. Care should be taken that the measure¬ 
ment from the periphery of the wheel to the top spar, 
measured, of course, in a vertical direction, shall be 
9 in. (see Fig. 113). 



-H O 

01 a 











































8 4 


MODEL AEROPLANES 


As twin gears of equal size are used, the torques 
of the oppositely revolving skeins of rubber will be 
balanced. Hence no bracing will be found necessary 
on the motor spar. The gearing, by the way, is bound 
to the top and bottom members of the fuselage with 
tinned iron wire, and soldered as shown in Fig. 115. 

The main plane is of rather a large span, and it 
is essential that birch be used, J- in. by 3 '^ in. in 
section. The wing spars are bent at their centres, to 
impart a tapering wing plan analogous to the Martin- 
syde monoplane. Seven ribs connect the spars, and 
these are cambered to J in. The wing tapers from 
10 in. at the centre to 7 in. at the tips, the centre 
rib projecting for J in. fore and after of the wing. The 
tin clips shown in detail in Fig. 119 slip over these, 
and so provide a means of adjustment to the centre of 
pressure of the complete machine. 

Choice of covering must be left to the builder; but 
yellow Japanese silk, proofed with varnish, will be 
found quite suitable, and of a rather pleasing amber 
hue. X birch kingpost passes through the fabric, and 
to this the wings are braced by No. 35 gauge music 
wire. Sufficient tension should be placed on the top 
wires to give the wings a 3-in. dihedral angle, as in 
Fig. 120. The detail illustration of the kingpost 
(Fig. 121) is self-explanatory. The bracing wires are 
anchored to wire hooks forced through the wing in the 
manner shown in Fig. 122. 

The correct position of the main plane should be 
found by trial. The kingpost can then be per* 
manently fixed to the main spar by pinning and gluing. 



TRACTOR MONOPLANE 


85 


No. 18 gauge wire of the music or piano variety 
should be used for the tail and rudder. Draw the 

4 

plan form of- the wing full size on a board; pins may 
then be driven partly home on each side of the line 
at spaces of about 3 in. The wire may now be pushed 
between the pins, cut off, and lapped for J in. The 
two cross ribs can be soldered to the tail before the 
tacks are withdrawn. It will be found on releasing the 
tacks that the wire will remain true to the shape of 
the template. This may seem a rather laborious 
process; but it is far quicker and easier than attempt 



ing to guess the correct curvature. The rudder may 
be made to any convenient shape, preferably that 
shown. The two ends should be sprung outwards 
after the form of the letter A to form a clearance for 
the rubber hooks, and then soldered to the tail. A. 
very slight adjustment of this will be found necessary 
to obviate propeller torque. 

No provision has been made for the adjustment of 
the lift on the tail. Indeed, none was found neces¬ 
sary, it being quite an easy matter to bend the tail 








86 


MODEL AEROPLANES 


daps np or down to increase or decrease the elevation. 
They should always, however, have a slight negative 
angle to maintain longitudinal stability. The tail 
should be bound to the fuselage with copper wire. 

The propeller, of the usual integral type, is carved 
from the solid block, which measures 15 in. by f in. 
by 2J in. It should be made of right-handed pitch, 
and must be placed on the right-hand gear, so that 
thrust balances torque. On each side, nine strands of 



J-in. strip rubber, lubricated with diluted soft soap, 
supply the motive power. This will stand approxi¬ 
mately 600 turns. Vaseline will suffice to minimise 
friction on the gears. 

It is advisable to test the model down the wind 
with about 50 per cent, of the maximum turns. The 
main plane should be moved forwards to increase the 
elevation, and backwards to decrease it. 

Fig. 123 shows the model in perspective. 





CHAPTER XII 


Hydro-monoplane 

The present machine is capable of making a flight 
of about sixty seconds after rising from the water, 
which it does after travelling from 8 ft. to 10 ft. undei 
normal conditions. This model is what is known as 
the “ A ” frame (see Chapter III.) type of mono¬ 
plane fitted with a. loaded elevator. 

The framework or fuselage is not constructed in 
quite the orthodox manner, but in the manner shown 
in section at d and e (Fig. 124). These side members 
are made from two pieces of best silver spruce 3 ft. 
3 in. long, f in. by J in. at the forward or elevatoi 
end, J in. by J in. in the middle, between the elevator 
and the main plane, and § in. by -ft- in. at the pro¬ 
peller end. This tapering is necessary in order to 
make the wood proportionate to the strain to which 
it will be subjected. This is called a cantilever. Aftei 
each stick lias been planed to the above sizes, a hollow 
chisel is used to channel out the wood on one side, the 
finish being given with a woodworker’s file. The 
opposite side is rounded off after the inside is finished, 
The front ends are bound together and glued, the 
forward hooks (to which the rubber is attached), and 
the protector, shown by Fig. 125, being incorporated 
at the same time; these are made of No. 18 and No. 20 

s.w.G. piano wire respectively. 

s 7 


MODEL AEROPLANES 


£8 


The other extremity of the fuselage is held 9J in. 
apart by means of a bamboo distance strut, measuring 
ft- in. by ft in. This strut, together with the three 
others, is carefully shaped, the ends sharpened, and 
then fitted into a split in the side members as indi¬ 
cated in Fig. 126. Considerable care is needed in 
making this form of joint; but when the joints are 
glued and bound over with J-in. strip silk, they are 
wonderfully strong. 

The propeller bearings are made of No. 18 s.w.G. 
wire, and resemble a lady’s plain hairpin bent at 
right angles midway, with a cupped washer soldered 
on the round end to take the thrust (see Fig. 127). 
These washers, known as French clock collets or 
cupped washers, may be procured at any watch re¬ 
pairer’s at 3d. per dozen. The propeller bearings 
should be bound to the fuselage at the same time as 
the end distance piece is fixed. The frame is trussed 
with two diagonal bracing wires; No. 30 s.w.G. piano 
wire should be used, this being strained with the aid 
of hooks as shown in Fig. 128. To tighten the wire, 
twist the hooks with a pair of round-nose pliers. 

The main plane is 37 in. in span, with a maximum 
width of 7 in. at the centre, tapering to 6 in. at 
3 in. from the tip. The camber is | in. at the centre 
and § in. near the tip. The frame is constructed of 
bamboo, the leading edge and the end ribs being one 
long piece of selected yellow bamboo, ft in. by ft in., 
and is bent to the shape by holding over an incan¬ 
descent gas burner. The trailing edge is made of 
similar material; but is straight when looked at in 






Fig. 129.—Rib Attachment Fig. 126.—Cross Member Joint 





































































go 


MODEL AEROPLANES 


plan. This piece measures 34 in. by A in. by A i n -» 
and is joined to the end ribs as shown at c (Pig. 129), 
afterwards being bound with strip silk. r lhe ribs 
are all ^ in. by i in, being bent in the manner 


suggested above and split-jointed into the spars. 

The main plane has a dihedral angle of 1 in 7 ; 
that is, the tips are about 2f in. higher than the 
centre of the plane. The plane is covered with 
proofed silk secured with fish glue. 

The elevator is a miniature edition of the main 
plane, being 13 in. in span and provided with a chord 
of 3J in. The camber is § in. at the centre and A in* 
at the tips. It is attached to the framework in the 
following manner: Two straight pieces of thin bamboo 
5 in. long are attached to the under-side of the elevator, 
and run parallel to the tapered end of the fuselage * 
and the projecting ends of these pieces are attached 
to the frame with elastic bands. To give an in¬ 
creased angle, blocks of wood are placed under the 
bamboo strips as shown in Fig. 125, these pieces being 
£ in. high. A greater or less angle may be given 
by moving the blocks either backwards or forwards as 
required. 

The floats are three in number, and are of equal 
dimensions, 6 in. by 2 in. by J in. at the greatest 
depth, which is about three parts of the way from 
the front. To construct the floats, two side pieces 
of A*i n - birch are cut to the shape given in Figs. 130 
to 131 a, and these are nailed to the ends of a piece 
of whitewood measuring 2 in. by J in. by £ in. Join¬ 
ing each end of the side pieces is a piece of white- 





Fig 130,— Side Elevation 


Fig. 134.- Rear Elevation 


Fig. 132.—Rear 
Float 


Fig. 133.—Screw Eye 






























Q2 


MODEL AEROPLANES 


wood, cut to fit so as to form a nice entry, the forward 
piece being flat on top and the rear piece flat on the 
bottom. At the place marked G (Pig. 130) there is 
an additional piece to strengthen the float and keep 
the silk covering taut. Running from front to back 
there is a J-in. by -j^-in. strip of bamboo to keep the 
silk from sagging when running on the water. The 
front floats are nailed to the bamboo cross-piece, and 
the adjustment is made by bending the small pieces 
of piano-wire F. The rear float attachment is shown 
by Fig. 132, and the adjustment is made in the same 



Fig. 135.— Model Hydroplane 


way. The wire is attached to the floats with small 
hooks as shown by Fig. 133, these being screwed into 
the distance pieces of the float. The connecting wires 
are bound to the fuselage with strip silk and glued. 
The flat portion of the under-side of the front floats 
has an angle of incidence of 1 in 6, the rear float angle 
being 1 in 8. 

Another type of float is quite practicable, if pre¬ 
ferred. 



HYDRO-MONOPLANE 


93 


The propellers are 10 in. in diameter with a pitch 
of 23 in., and are carved from a solid piece of 
mahogany. The blades are glasspapered to a thick¬ 
ness of about A in., and are strengthened with silk 
stuck on one side. 

The floats are covered with the same proofed silk 
as the planes; but to ensure complete impervious¬ 
ness to water, coat with a mixture of 2 parts of boiled 
oil and 1 part of gold size. Fig. 134 is a rear elevation. 

The main plane rests flat on the fuselage, #nd is 
held in place by means of two 9-in. by J-in. by i^-in. 
pieces of bamboo, which are secured to the framework 
with elastic. This method allows the plane to be 
readily removed. There are six strands of thick J-in. 
strip elastic to each propeller, and the number of turns 
given is about 900 when well lubricated. 

The total weight of the complete model is only 
6 oz., and in making the machine every effort should 
be made not to exceed this amount. 

Fig. 135 shows a model hydro-monoplane in per¬ 
spective. 


G 


I 



CHAPTEK XIII 

Compressed-air Engine for Model Aeroplane 

Signs are not wanting that compressed air as a motive 
power for model aeroplanes will become equally as 
popular as the twisted skein of rubber, which has prac¬ 
tically held the field since it was introduced about the 
year 1870 by Alphonse Penaud. 

One of the chief disadvantages of the rubber motor 
is that experiments of a full-size scale nature cannot 
be undertaken, owing to the length of frame required 
in order that the necessary power and duration of run 
may be obtained, and also owing to the disposition of 
weight, and consequently of the centre of gravity, not 
being tantamount to that obtaining in full-size prac¬ 
tice. With a compressed-air plant these disadvan¬ 
tages are eliminated, since the weight can be kept well 
forward, thus making possible the designing of a model 
which represents in essential proportions a full-size 
machine. 

Particulars are here given of a highly successful 
plant, for which the machine described in the next 
chapter was especially designed. Several of the illus¬ 
trations in this present chapter are exaggerated to 
render the construction clear, and it is thought that 
the details given will be found, comprehensive. 

Pig. 136 gives a plan view of the engine, which is 

94 



Figs. 136 to 139.—Arrangement and Details of Engine 

















































































































































9 6 


MODEL AEROPLANES 


rotary with, of course, a stationary crank-shaft. The 
five cylinders are soft-soldered to what may be termed 
the crank-case, which consists of two circular brass 
discs of the gauge indicated. In order that the 
cylinders may he accurately located round the plates, 
a wooden jig should be made with slots to receive the 
cylinders, and a recess to take the plate. Five lighten¬ 
ing holes are drilled in the two plates as shown. The 



i 


*- £ 


IjAX . 


% 1 13AX 




Fig. 140. Details of Crank 


Fig. 142.—Connecting Rod 





Fig. 143.— 
Piston Tongues 


Fig. 141.—Section of Cylinder 


front plate, that is, the one carrying the propeller bolt, 
is, however, left off until the pistons, crank-shaft, and 
sleeve are assembled. 

Fig. 137 gives a side elevation of the engine, with 
the crank-shaft and sleeve shown in section. It will 
be seen that the sleeve butts to a shoulder, a slight 
undercut being given to the shaft when turning this 





















































ENGINE FOR MODEL AEROPLANE 97 


portion to ensure a good joint. From this figure the 
inlet and exhaust principle will be manifest. It will 
be noticed that as each inlet pipe coincides with the 
right angular inlet in the shaft, so does it receive a 
charge of compressed air. The pressure on the piston 
revolves the engine, thus shutting off inlet to that 
particular cylinder and bringing the next cylinder in 
line with the inlet. As soon as the first cylinder 
nears the bottom of its stroke it begins to exhaust 
through the diametrically opposed exhaust port. 
Needless to say, the crank-shaft and sleeve must be 
turned a good running fit, otherwise there will be 
considerable waste of power. The best method to 
employ is to turn the shaft a push fit within the 
sleeve, and then to grind it in with rottenstone. When 
soldering the inlet pipes into the sleeve, care must be 
taken to ensure that they do not become “ choked 
with solder. The sleeve should afterwards be 
reamed out to remove all superfluous solder. When 
soldering the sleeve into the back plate care must also 
be exercised to ensure that it is truly at right angles 
to the plate. 

It must be clearly understood that the engine re¬ 
volves with the sleeve as a bearing. The five holes 
which are drilled round the sleeve to receive the inlet 
pipes must be equidistant, so that the periods of inlet 
are synchronous. 

Fig. 138 gives an enlarged view of the crank¬ 
shaft and sleeve, and is self-explanatory. Observe 
that the exhaust port is larger in diameter than the 
inlet. 




9 8 


MODEL AEROPLANES 


Details of the pistons are shown by Fig. 139. The 
connecting-rods are soldered to tubular distance pieces, 
which rock on the ^--in. silver-steel gudgeon-pins, 

which pass through the pistons, 
being cut shorter than the outside 
diameter of the piston to avoid 
possible scoring of the bore of the 
cylinders. The gudgeon-pins are 
soldered into position, the super¬ 
fluous solder being scraped from the 
piston walls. To ensure airtightness 
of the pistons and cylinders, cupped 
leather washers are fixed to the 
piston - heads by means of tin 
tongues soldered to them, and 
which are forced through the washer 
and bent over. The ordinary cycle- 
pump washer is admirably suited to 
the purpose, but the height of the 
washer when within the cylinder 
should not exceed J in. 

Fig. 140 gives dimensions of the 
crank and throw, to exaggerated 
scale, to avoid crowding the details. 
The important point to bear in mind 
when beginning this portion of the 
construction is to obtain the correct 
stroke, since the cylinders are designed to take 
a stroke of J in. only. See also that the crank-pin 
revolves truly, that is, at 180° to the shaft. 

Fig. 141 is a longitudinal section of the cylinder. 
























ENGINE FOR MODEL AEROPLANE 99 


As there shown, the cylinder-head is “let in ” the 
head and soldered there. The inlet pipes should 
be packed with resin prior to bending, this being after¬ 
wards melted out. The connecting rods are shown by 
Fig. 142, the important dimension, obviously, being 
the centre distance of the holes for the crank-pin and 
gudgeon-pin respectively. These are of No. 20 b.w.g. 
brass. The tin clips used to secure the cupped leather 
washers to the piston head (four of which are used 
for each piston, so that twenty in all will be required) 
are shown by Fig. 143. They are of No. 30 s.w.g., 
and are bent along the dotted line to a right angle, 
the J-in. portion being the end to be soldered to the 
piston. 

The compressed-air container shown by Fig. 144 
is made from copper foil of the thickness shown. This 
is folded round a wooden former of circular cross- 
section, and tied tightly in place while the lapped 
joint is being soldered. The two faces of the joint 
that are in contact should first be tinned, using 
Fluxite or resin as a flux; spirits of salt should on no 
account be used, as this has a deleterious effect on 
metal of so fine a gauge; and a mediumly heated iron 
should be used to solder the joint. 

Wind the body with the No. 35 s.w.g. piano wire, 
soldering each spiral at each revolution so that it 
maintains its correct pitch. Now attach one of the 
half-balls (which for preference should be provided 
with a stepped flange as shown) while the body is 
still on the wooden former, first tinning the two sur¬ 
faces in contact, and then “ running ” the solder 



100 


MODEL AEROPLANES 


round with a mediumly heated soldering-bit, and so 
sealing the joint. Prior to attaching the second half- 
ball to the other end, a tension wire must be attached 
to the flange, either of the valve or the tap (according 
to which half-ball was attached first), by soldering. 
This is then passed through the body of the container 
(the wooden former, of course, now having been re¬ 
moved), and threaded through a hole drilled in the 
half-ball at a convenient point near the centre. Ten¬ 
sion is now applied to the wire and the second half¬ 
ball eased into position, and while still pulling on the 
wire it is soldered into the hole through which it 
passes, afterwards being cut off sufficiently long to 
form a coil on the end. 

It will, of course, be clear that the valve (of the 
Lucas type) and tap are soldered to the half-ball before 
the latter are affixed to the container body. 

The container should be inflated and immersed in 
paraffin to test for leakages, and when these are 
stopped up the container and engine may be connected 
by a short length of tubing. The engine is then ready 
for running. Thin machine oil should be used for 
lubricating purposes, and where necessary the con¬ 
necting-rods must be staggered for clearance. 

In conclusion, it should be pointed out that the 
plant should not weigh more than 10 oz. complete, and 
is capable of flying a machine weighing 2 lb., provided 
that it is efficiently constructed. The container should 
be inflated to a pressure of not less than 100 lb. 
Pig. 145 shows a similar compressed-air model aero¬ 
plane engine complete. 


/ 


i < 


< 
















102 


MODEL AEROPLANES 


The accompanying photographic reproduction 
shows a model compressed-air plant for model aero¬ 
planes which is similar in general design to the one 
illustrated. The difference is that inlet takes place 
through hollow connecting-rods, which are ball-ended 
and fit into ball seatings. The cylinders oscillate, and 
the connecting-rods, being rigidly attached to the 
pistons, by their angularity during revolution form 



Fig. 145.—Three-cylinder Engine 


the inlet and exhaust mechanism. The propeller is 
geared up in the ratio 2:1. 

The design is analogous to a very early French 
engine much in evidence in the early days in model 
experiments. 

It is thought that the photograph will give the 
reader an idea of the general arrangement of the plant 
previously described. 

Driving Small Biplane,— Fig. 145 is a front eleva¬ 
tion, with the front plate removed, of a 3-cylinder 











ENGINE FOR MODEL AEROPLANE 103 


engine on similar lines, which would be sufficiently 
powerful for models up to 12 oz. weight. As will be 
obvious, the three cylinders are fixed (by solder) to 
two circular discs of No. 20 gauge brass forming the 
crank chamber. The cylinders and various component 
parts should be assembled before the front plate is 
fixed. A length of brass tube is soldered into the back 
plate, and equidistant round its periphery three J-in. 
holes must be drilled to receive feed pipes which pass 
to the cylinder heads. A piece of brass rod to form 
the crank-shaft must be turned to make a good running 
fit within the tube and inlet, and exhaust holes drilled 
as indicated by the dotted lines. The pistons should 
be made an easy fit. Pieces of by-pass tubing are 
soldered into the small ends of the connecting-rods. 
Through these tubes pass the gudgeon-pins which 
are anchored to the piston walls. The position of 
the connecting-rods in relation to the piston is thus 
maintained. The container (into which air is com¬ 
pressed with a foot pump to from 100 lb. to 120 lb. 
per square inch) is constructed from copper foil of 
three-thousandths (’003) of an inch thickness, and is 
of the same dimensions as the five-cylinder one. 



4 


CHAPTER XIY 

Biplane Driven by Compressed-air Engine 

The model aeroplane illustrated by Fig. 148 has been de¬ 
signed to suit the compressed-air plant fully illustrated 
and described in the preceding chapter. It is from 
the results obtained from the testing of the plant that 
the dimensions of a suitable model for it are deter¬ 
mined ; and while the design may suit the majority 
of the plants constructed from the illustrations shown 
in pp. 95 to 101, it is chiefly given to show the correct 
method of designing a “power-driven” machine, 
since the power unit (unlike the elastic motor) cannot 
be varied, and recourse to some established line of 
reasoning becomes essential. 

The first thing to do, then, once the plant has been 
“tuned up,” is to ascertain the thrust obtainable 
from it. This is found by suspending the plant by 
the valve on a balance, with a container fully inflated, 
the weight registered being carefully noted. The 
container pressure should now be released, and the 
weight registered when the motor is running observed. 
By subtracting the former from the latter the thrust 
is obtained. 

Thus, assuming the plant, at rest, to weigh 8 oz., 
and when running 12 oz., it is clear that the thrust 
is equal to 4 oz. Now, it is necessary to know the 
average thrust developed, since, as hitherto explained, 


BIPLANE DRIVEN BY ENGINE 105 


the thrust is not constant, but gradually diminishes 
as the density of the air in the container approaches 
normal atmospheric conditions; that is, 14'6 lb. per 
square inch (known as an atmosphere). It is possible 
to obtain some very interesting data by plotting a 
graph of the thrust given off at various moments from 
the release of the pressure in the container. Mean¬ 
while it can be taken as a good rule that the thrust 
registered after one-third of the effective run of the 
motor represents approximately the average thrust; 
and the figure given above (4 oz.) will serve for the 
purpose of illustration. 

It is next, necessary to know the weight of the 
model it will lift. It is well established that a plant 
will fly a machine weighing from four to six times the 
weight of the thrust it develops, although, of course, 
much depends on the efficiency of the model; the 
greater the complexity of frame members the lower 
the lift drag ratio, and consequently the lower the 
ratio between the thrust and the weight of the model. 
Compromising, and taking 5 : 1 as the ratio, 20 oz. is 
obtained as the total weight of the plant and model. 

The next point to be decided on is the loading, 
and as the model is to be a biplane a comparatively 
light loading can be used. In the case of the machine 
shown in side elevation by Fig. 146 and in front eleva¬ 
tion by Fig. 147, 4 oz. has been taken as the loading 
per square foot. Bo that the total area of the wings 

20 

will be ~r = 5 sq. ft. = 720 sq. in. A span of 54 in. 

4 

for the top plane and 46 in, for the bottom one has 



io6 


MODEL AEROPLANES 


been decided on, and by using a chord of 8f in. the 
total area of the wings vies very approximately with 
this figure, allowing a small margin for excess weight. 
The area of the tail, which is non-lifting, need not be 
taken into account. Although the “ gap ” is given 
as being equal to the chord, it could be made, if any¬ 
thing, j- in. greater. 

Now with regard to actual materials. Birch is to 
be used for the longitudinals, straight in the grain 
and of the cross sections illustrated. The lower 
member is bent under steam to the curvature shown 
—of 6J-in. radius. Two vertical struts support the 
wings, and these should be cut from hickory. A short 
tie-strut secures the bottom longitudinal to the front 
inter-strut, the joint being made by means of side angle- 
plates bound into place. It will be found good prac¬ 
tice to make a full-size drawing of the machine in side 
elevation, so that it can be used as a template to fit 
up the cross members—particularly with regard to the 
cutting of the angles. 

The joint of the longeron to the cross member is 
shown separately at A (Fig. 146). The usual fish¬ 
plates are employed, so made that a small wiring plate 
is left protruding from the binding, to which the 
cross-sectional and longitudinal-sectional wires are 
made off. 

The plant itself is slung into the framework by 
means of eight wires, each being made off to the 
wiring plates. Each should also be provided with a 
small f-in. wire strainer to enable the plant to be fixed 
quite rigidly—albeit permitting of its being removed 



BIPLANE DRIVEN BY ENGINE 107 


for inspection or repairs. The wires from the engine 
itself are taken off from the four small eyes soldered 



to the stationary portion of the crank-shaft. Great 
care should be taken to ensure that the plane of rota¬ 
tion of the screw is at right angles to the main planes. 





































































io8 


MODEL AEROPLANES 


A lj-in. dihedral is given to the bottom plane by means 
of the bracing wires passing between the inter-struts, 
and shown on the preceding page. 

It has been thought advisable to attach a small 

rear wheel, to enable the 
model to rise off the ground 
with as little loss of power 
as possible. Such a wheel, 
with attachments, need 
weigh no more than J oz., 
and is a great improvement 
over the cane skid usually 
employed. 

In bracing the outriggers, 
or longerons, some care will 
be required to ensure their 
being quite true. It will be 
easier to finish each section 
off first, so that they are 
quite parallel at the joints. 

The part plan view of the 
model (Fig. 148) will make 
the relative position of the 
various component parts 
quite plain. The two top 
tail outriggers pass through 
the fabric at the point where 
the spar is located, their front ends being pinned and 
cross bound to the wing spar, which is made of greater 
cross section in the centre, so that its strength is not 

materially impaired through the piercing of it. Birch 













































































BIPLANE DRIVEN BY ENGINE 109 


is to be used for the wing spars and ribs of the sections 
indicated. 

The planes are ribbed at periods of 6 in. and given 
a camber of f in., the greatest depth of which is 2J in. 
from the leading edge. It is far easier to impart the 
camber after the wing framework is made than to 
camber each rib separately. Each rib should be cut 
1 in. longer than necessary, and pinned and glued to 
the spars, with j- in. overlapping each of these latter. 
When the glue is quite set, the pins may be clinched 
over by supporting the wing on an iron weight and 
tapping them back flush to the spars. 

The full-size section of the camber should be drawn 
upon a board, with which to check the accuracy of 
the first rib to be cambered (the end rib). 

The ribs are cambered in a jet of steam, the convex 
or top sides being placed nearest to it. Having cam¬ 
bered the end rib carefully to agree with the drawing, 
the others may be matched to it. It will thus be easy 
to ensure that every rib is of the correct curvature, as 
any mistake in the steaming of the rib will distort the 
wing spar at the point of its attachment. 

If, however, it is thought advisable to camber the 
ribs first, a wooden bending jig should be made, to 
enable several ribs to be bent at one operation. The 
ribs should be tied down to the jig with string, and 
thus held under the steam jet, being well dried in front 
of the fire before they are'detached from the jig. All 
three spars pass underneath the ribs. 

A very light fabric should be chosen, such as can 
be obtained from the model-aero accessory warehouses, 



no 


MODEL AEROPLANES 


or an unproofed Japanese silk can be used and var¬ 
nished when on the wing. If this latter is used, it 
will be found advantageous to use a yellow hue, as this 
colour is least affected by the action of the varnish. , 
But the covering of the wings must be left for the time 
being, for the reason that the sockets to which the 
inter-struts are made fast must first be attached. 
Further, the top plane must be covered after the tail 
outriggers have been assembled, as it is so much easier 
to make the joint between the wing spars and these 
latter before the fabric is attached. 

To render it unnecessary to refer to the point 
further, it may be noted that the fabric is brought over 
the leading spar of each wing to pocket it out. It is 
much neater to sew the fabric along on the leading 
edge, as when glue is used an unsightly black smear 
shows through. The fabric should be stretched from 
end to end first, the fabric overlaps being glued on the 
bottom face of each end rib. Drawing-pins should be 
partially pressed into the ribs to secure the fabric until 
the glue is set. 

At b in Fig. 148 is shown the method of securing 
the bottom plane to the inter-struts. Convenient 
notches are cut in the struts into which the plane is 
sprung. It will have been noticed from the side eleva¬ 
tion (Fig. 146) that the width of the inter-struts in¬ 
creases towards the bottom or lower ends, and also that 
they incline slightly; this is to provide for the entry 
of the lower plane, since the top plane is attached out¬ 
side the struts, while the bottom is placed inside them. 
At c is shown the method of attaching the inter-struts. 



BIPLANE DRIVEN BY ENGINE hi 


The tail is built up from split bamboo, J in. by 
: /‘ $ a in. in cross section, and the rudders are framed up 
from No. 20 gauge piano wire. The ends of the rudder 
frames are forced through the longerons, and the ends 
bent back in alignment with them; they are then 
bound to the longerons with black three-cord carpet 
thread. The rudders are covered after being fixed to 
the outriggers. When it is necessary to adjust them, 
the piano wire will be found sufficiently ductile to 
admit of a warp being placed thereon. 





Model 


Eleven ribs connect the spars of the top plane and 
nine those of the low T er, the camber of each being the 
same; that is, the same depth of camber is maintained 
throughout. Before the wings are covered, the angle- 
plates to which the inter-struts are fixed must be 
bound on; and these are cut from No. 30 gauge sheet 
tin. They should be cut less in width than the spar 
to which they are attached, in order that their sharp 
edges shall not cut through the binding. To prevent 
the plates from moving, they should be lightly sunk 












































112 


MODEL AEROPLANES 


into the wing spar with two centre-punch dots, and 
a film of glue should also be spread over the face of 
the plate coming in contact with the spar. 

The inter-struts are stream-lined in cross section 
(see Fig. 149); but they are to be left rectangular in 
section at their ends, to provide a flat surface for the 
plates to bed home on. The ends of the plates are 
turned back over the binding, which may be of the 
light machine variety. 

The lower ends of the inter-struts are cut off to the 
same angle as the dihedral on the lower plane, to 
avoid distortion of the plane. Spruce or American 
whitewood may be used for them, the greatest cross 
section being J in. by J in. The greatest cross section 
is situated at the middle of the strut, whence it 
tapers to ^ in. by J in. Fig. 149 shows the attach¬ 
ment of the inner strut to the wing spar. In Fig. 150 
are shown the brackets forming the guides for the 
axle, and also the supports for the rubber shock- 
absorbers. Piano wire is used for them. The width 
of the guide should be such that the umbrella-ribbing, 
which constitutes the inner portion of the axle, rides 
freely within it. The wheel axles are cut from No. 16 
gauge piano wire, and they are soldered to the um¬ 
brella-ribbing, being sunk into the channel of the 
latter, bound with No. 30 gauge tinned iron wire, and 
then soldered. 

Ordinary elastic, as used for a rubber-driven model, 
can be used as the shock-absorber, and it should be 
neatly and fairly loosely bound to the vertical guide, 
the axle of course being first seated therein. In 



•- •CD 'Ol '© 0 -h > 0 *) 

S-Jfcfc 2fe 

« 

• Q 






























































114 


MODEL AEROPLANES 


order that the absorber brackets may maintain a ver¬ 
tical position, their ends are shaped to a form similar 
to the letter U. They are wire-bound to the skids 
and lightly soldered. 

The bottom plane only must be covered; it will be 
easier to cover the top plane when the machine is 
assembled, for it would be a difficult matter'to secure 
the top outriggers to the spars were the fabric attached. 

Having assembled the outriggers and completed the 
bracing of it, it will be possible to attach it to the 
wings. 

Small elliptical holes are cut in the fabric of the 
lower wing, through which the central supports or 
stanchions pass, and the bottom plane is seated home 
in the notches alluded to in Fig. 148. Next, the top 
outrigger ends are fitted up, being cut off to correct 
length and halved on to the wing spars, as shown in 
Fig. 151. The vertical support is then glued, pinned, 
and cross-bound to the outrigger. 

Great care will be necessary to ensure that the 
outriggers are quite central with the planes. A point 
to be made clear is that if in the fitting of the top 
outriggers one is cut even in. short, the tail.end of 
the machine may be § in. out of centre. In order to 
check inaccuracy in this direction it would be advisable 
to mark the centre of the horizontal tail member, 
insert a drawing-pin, and take the measurement to the 
corner of the wing tip, on both sides of the model; 
the outriggers should be temporarily lashed to the 
wing spars, and gradually adjusted until they are 



BIPLANE DRIVEN BY ENGINE 115 


located centrally with the planes.. Perhaps it may be 
interesting to here mention that this is the method 
employed in locating the fuselage of full-size machines. 

The bracing of the planes should now be under¬ 
taken. All lift wires should first be fixed, beginning 
from the wing tips. Just sufficient tension should be 
placed on each wire to ensure rigidity. A wooden 
straightedge should be used to reveal any distortion 


Fig. 158.—Biplane Driven by Compressed Air 



of the spar. The top plane must be given a slight 
dihedral, so that when the anti-lift wires are inserted 
it assumes a perfectly parallel position. 

The upper and lower longerons are spanned at 
the tail end with light spruce cross-bars, J-in. by 
J-in. section, which are let into mortises cut in the 
longerons; and two vertical posts are halved on to 
these cross members (see Pig. 152), to provide the 

















n6 


MODEL AEROPLANES 


fulcrum about which the tail swings in the quadrant, 
to be referred to presently. They are spaced 4 in. 
apart, which is equivalent to the distance between two 
ribs; and on the outside of them a groove is cut in 
the centre of each to provide a seating for the two 
central tail ribs. These grooves must be cut V-shaped, 
the apex of the V facing the trailing edge of the post. 
The object of the groove is to form a guide for the tail 
when it is desired to alter the angle of it. A pin 
should be driven through the rib and into the groove 
to constitute the pivot on which the tail swings; and 
the ribs must be bound with fine thread on each 
side of the pin to prevent the rib from splitting. 
It will be found that it is better to bind the ribs before 
inserting the pin. 

The central inter-struts are attached to the skids 
by angle-plates, and in Fig. 153 the form of these is 
given. It must be understood that there are two 
plates to each joint, one on each side of it, and for 
neatness and simplicity they can be cut from one piece 
of tin, both plates being thus formed in the one. 
No. 30 gauge tinplate is suitable. The plates are 
pinned, clinched, and bound into place, and constitute 
an exceedingly rigid piece of construction, which is 
■needed in this portion of the machine, bearing as it 
does the impact of landing. Glue should be neatly 
brushed into all the joints. The tie . strut is to be 
stream-lined as far as practicable without materially 
impairing the strength of it. 

A very neat finish can be given to the binding if 
it is just brushed round with japan black, which shows 



BIPLANE DRIVEN BY ENGINE 117 


up in pleasing contrast to the light brown varnish with 
which the framework is coated. 

Fig. 154 gives the shape of the quadrant, which 
makes possible the variation to the angle on the tail. 
It is cut to a radius of 4 in., and is pinned into 
position. The pitch of the teeth is J in., and this 
facilitates a very fine adjustment. It should be so 



Fig. 159. — Compressed-air-driven Monoplane 


fixed that the tail springs tightly into notches, but 
not so tightly as to render adjustment difficult. Trial 
and error will be found the best method of locating 
its position. 

It was mentioned in the preceding chapter (see 
pp. 94 to 103) that the axle is composed of two portions, 
umbrella-ribbing and piano wire, and Fig. 155 shows 
the construction. It will be seen that the piano wire 
beds into the channel (which is fixed in a trailing 
position), wherein it is bound and soldered. The 




n 8 MODEL AEROPLANES 

wheels are spaced apart by means of small brass-tube 
collars, soldered to the piano-wire axles in their 
respective positions. The axle itself, as mentioned 
earlier in the chapter, is attached between the shock- 
absorber brackets, being held there by means of suit¬ 
able radius wires secured to any convenient part, the 
rubber binding forming the absorber. The radius wires 
are essential in order to maintain the lateral position 
of the axle relatively to the planes. Sufficient rubber 
binding is to be used to absorb the shocks the model 
is bound to receive, the exact quantity, of course, being 
impossible to define. 

The rear wheel members are fixed to the longerons 
in the following manner. The ends are bent back 
parallel to align with the frame member. The apices 
of the V chassis members are soldered to the short 
axle carrying the back wheel, the axle being cut a 
length suitable to the hub of the wheel. No. 20 gauge 
wire is used for all portions of the rear chassis. Fig. 
156 makes this clear. 

Fig. 157 shows the joint of the trailing central 
inter-struts to the top longeron. It will be seen that 
the joint is a halved one, pinning and binding forming 
the security. 

All woodwork may be polished by filling the grain 
with gold size, and finishing with a good varnish. 

In flying the model the writer would point out that 
full pressure should not be given to the plant until 
adjustment has been completed, also the importance 
of tuning the machine by starting it from the ground, 
thus obviating many vexing smashes. Further, the 



BIPLANE DRIVEN BY ENGINE 119 


rudder must be set to counteract torque; if the screw is 
of left-hand pitch, then torque will tend to bank the 
machine to the right, and the rudder must therefore 
he set to the left, and vice versa. 

A sketch of the finished machine is given by Fig. 
158, and a design for a monoplane driven by the same 
plant in Fig. 159. 



CHAPTER XV 


General Notes on Model Designing 

Calculations in Designing a Plant for a Model Aero¬ 
plane. —The correct method to adopt in designing a 
model is to build the machine exclusive of the motor, 
weigh it, and design the plant to suit; or to build the 
plant first, determine the thrust it develops, and vary 
the dimensions of the machine (and hence the weight) 
to suit. 

It can now be taken as a general rule that a plant 
will fly a machine three times the weight of its thrust. 
Hence a plant developing 3-oz. thrust would fly a 
machine weighing 9 oz. or 10 oz. But, since the thrust 
of a compressed-air engine is not constant, gradually 
diminishing as the pressure in the container grows less, 
for a machine weighing 9 oz. (assuming the machine 
to be built first) the plant will require to develop about 
5 oz. initial thrust. The diameter of the propeller is 
dependent on the most efficient speed of the particular 
motor employed. 

Assuming that the model does not weigh more than 
17 oz., a four-cylinder engine constructed would an¬ 
swer admirably. It would require a container 24 in. 
long and 3 in. in diameter, constructed of copper or 
hard drawn brass foil '002 in. thick. Should, however, 
the reader particularly desire to fit a rotary motor, 


120 


NOTES ON MODEL DESIGNING 121 


doubtless the five-cylinder rotary previously described 

will suit. 

Building Scale Models. —The great difficulty in 
building scale models to fly with rubber motors is to 
get the centre of gravity in the same relative position 
that it holds in the prototype. This is due to the long 
length of rubber-motor required to give the requisite 
power, and also to ensure a reasonable time-length of 
flight. 

It is in connection with the fixing or arranging of the 
rubber motor that the most radical departures in the de¬ 
sign of the prototype will have to be made, although 
the writer has evolved an arrangement whereby even 
this need not entail much departure from the lines of 
the original. This arrangement consists in providing 
a separate strut or frame to take up all strain from the 
rubber, it only being necessary to arrange suitable 
fastenings for the strut, which may take the form of 
clips, so making it possible either to remove the motor 
for the purpose of changing or repairing the rubber, or 
substituting a motor of different power or length. This 
is a great advantage on tractor monoplanes (with the 
main plane in front), where the rubber is more or less 
inaccessible by reason of the closed-in frame or fuselage 
of the machine. Another important advantage to be 
gained from the use of a detachable motor is that its 
position fore and aft on the machine can be varied, in 
order to bring the centre of gravity into the proper 
position to obtain correct balance, or, speaking with 
more technical accuracy, to make the centres of 
pressure and gravity coincide * 



122 


MODEL AEROPLANES 


With regard to the type of motor to adopt, this 
depends very largely on the machine which is being 
modelled. Whenever possible it should be of the 
simplest possible kind, consisting of the main strut to 
take the tensile strain, compressive, of course, so far 
as it affects the strut, and the torsional strain put on 
by the twisting of the rubber. At one end of this strut 
a hook of wire or other form of metal is formed to hold 
the rubber skein, whilst at the other end is fixed a 
plain bearing. Through this the propeller spindle is 
passed, having a hook at its end, over which the other 
end of the rubber is placed. 

On certain types such a simple motor is not possible. 
In order to concentrate the weight more at one point, 
the rubber and its struts have to be shortened; and to 
get the necessary number of revolutions of the pro¬ 
peller a gearing of two to one, three to one, or four to 
one, as the case may be, must be used. By this 
means the small number of turns which can be got on 
a short thick skein of rubber of great power will still 
give the number of propeller revolutions required to 
make a good flight, just the same as with a motor of 
ordinary thickness and of great length. Of course, 
some power is lost in the gearing. 

To resist fuselage distortion the spar must be suit¬ 
ably braced in a lateral direction , the outrigger carrying 
the bracing wires being situated just forward of the 
centre of the spar. No. 35 s.w.g. is quite strong 
enough for fuselage bracing. Silk fishing-line or 
Japanese silk gut is admirably suited for wing bracing, 
and is not so liable to stretch as the tinned iron or 



NOTES ON MODEL DESIGNING 123 


brass wire sometimes used. Piano wire is generally 
used for elevators, tail planes, chassis, and propeller 
shafts, of a gauge ranging from No. 17 s.w.g. to No. 22 
s.w.G. A clock-spring or piano-wire protector fitted to 
the nose of a model aeroplane will also prevent a 
broken spar should it strike some object such as a tree 
or wall during flight. 

The Kite and Model Aeroplane Association, which 
is the paramount body to observe and control model 
flying in England, and which is recognised by the 
Koyal Aero Club, stipulate that protectors must be 
fitted to nil machines competing in their contests. 



f 

<v 


CHAPTER XYI 

General Notes 

Stability .— The principles underlying the design of 
a successful flying model aeroplane are almost, if not 
quite, as complex as those involved in the planning of 
full-size machines. In some respects perhaps this is 
more so, owing to the fact that models must be prac¬ 
tically automatically stable both longitudinally and 
laterally, since they are not under any sort of control 
after they have left the hands of the person flying them. 
The adjustments to produce this automatic stability 
must be made before the machine is launched, and the 
fact that there are models which are capable of flying 
distances of several hundreds of yards, and high up in 
the air, is evidence that it is quite possible to make this 
adjustment accurately. 

A useful rule to remember is that to produce a longi¬ 
tudinally stable effect, the leading plane should make 
a greater angle (that is, a positive angle) than the 
following plane. And that conversely a condition of 
instability is set up when the leading plane makes a 
negative angle to the trailing one (see Fig. 160). 

Referring now to lateral stability, the same prin¬ 
ciple applies, although in the case of biplanes stability 
to a great extent can be obtained in another way. 

V 

Monoplanes and sometimes biplanes are made 

124 


N 


GENERAL NOTES 


125 


stable by what is known as a dihedral angle shown by 
Fig. 161, which represents the usual method of shaping 
the planes. This last-mentioned figure is intended to 
represent a front (or back) view of the machine. In 
aeroplanes of this type the elevator or tail, whichever 



is employed, may also be given a dihedral, though this 
is not often done. 

Lubricant, —A good lubricant can be made from 
pure soft soap 4 parts, pure glycerine 2 parts, water 

1 













126 


MODEL AEROPLANES 


6 parts, these constituents being boiled together to the 
consistency of syrup. 

Another excellent lubricant is made from castile 
soap 1 part, boiled in water 3 parts. Add black lead 
or plumbago sufficient to make a thin p&ste. 



Fitting Skid. — Steel wire skids can be fixed to 
model aeroplanes as in Figs. 162 and 162a. The wheels 
can be obtained of any model aeroplane firm, and can 
be fixed to the machine as shown in Fig. 163. This 
would increase the weight of the machine, and more 






















GENERAL NOTES 


127 


rubber may have to be used and the main planes 
adjusted to suit. Use No. 21 b.w.g. wire (steel). 

Elevator Adjustment. —Elevators are sometimes 
fixed to the fuselage as shown in the accompanying 
sketch (Fig. 164), which shows it fixed above the spar. 



Fig. 165.—Fixing Struts to Biplane 


Elevator 


/ 

Protector 



Wire Support 


m 


Thread 


\ 


Motor Rods 
Fig. 164.—Elevator Adjustment 


It is claimed that, in this position, the elevator is more 
efficient. 

Loading per Square Foot, —Generally speaking, 
the loading per square foot of supporting surface for 















































128 


MODEL AEROPLANES 


rubber-driven models should not exceed 6 oz., nor be 
less than 3 oz., while to obtain good stability the ratio 
of machine length to span should be somewhere in the 
neighbourhood of 3 : 2. 

Fixing Struts to Biplane.— One very suitable 
method of attaching the inter-struts to wings of model 
biplanes, that admits of dismantling the model for 
packing, is shown at a (Fig. 165). A short length of 
brass tubing of^-in. bore is bound w T ith fine florist’s 
tinned iron wire to the wing spar, the inter-struts being 
bent to the shape given at b, so that they spring tightly 
into the sockets. A simpler method is illustrated by c. 
Here the inter-struts are bent at right angles on the 
ends, bound to the wing spar, and soldered. Much 
will depend on whether a fuselage is one- of two- 
membered, but a frame attachment capable of adapta¬ 
tion to either is given by d and e. Wire crutches are 
bent to take the cross section of the frame member or 
members, and fixed by binding and solder to the central 



Fig. 166.—Water-Surface Hydroplane 


inter-struts. Yet another method is shown at F, which 
is self-explanatory. 

Water-surface Hydroplane. —For a water-surface 
hydroplane 3 ft. long try a breadth of 11 in., same 
beam all the way. Make the depth 2J in. at the stem 
and 3 in. at the step. The step may be f in. deep, 










An efficient Section 




Stepped 

Fig. 167.—Sections of Hydroplane Floats 





















130 


MODEL AEROPLANES 


and would be placed about 15 in. from the stern. The 
writer would suggest fins as shown by dotted lines in 
the accompanying illustration (Fig. 166) for steering 
purposes, one fin on each side at the stem, and one on 
the centre line forward. The fins should be made of 
thin aluminium and be quite sharp on the edges. 
Canvas would be too rough a surface, producing too 
much skin friction; oiled silk would be better, but the 
writer would recommend thin wood, french polished. 
The power needed to make these boats “plane ” is 
very great, and considerable difficulty might be ex¬ 
perienced in getting any distance out of it with 
clockwork. 

Calculating Capacity of Hydroplane Floats. —The 

floats of a model hydroplane must be made sufficiently 
large to displace about three times the model’s weight 
of water, since it is necessary that they should be only 
one-third immersed. A cubic foot of water weighs 

1728 8 

1,000 oz. approximately. Then ^qqq x y = 13'8 cub. 

in. must be displaced to float 8 oz. Multiplying this 
by three gives 42 cub. in. as the total cubic capacity 
of the floats. Two front floats, each 5 in. by 2 in. by 
1 in. maximum depth, and a rear float 8 in. by 3 in. 
by 1 in. would be about the correct size to use. A 
slightly larger diameter and pitched propeller would 
be necessary on a hydroplane to develop more thrust 
to overcome the resistance of the floats. Some well- 
known hydroplane sections are given in Fig. 167. 

Waterproofing Silk for Model Aeroplanes. — A 
waterproofing solution can be made of pure coach 




Showing Marking of Block 



Finished Screw of Truly 
Helical Formation 



-3 tflG* Diam 


Setting-out the Angles 


Cross Section 



Showing Halving of Block 


Fig. 168.—Four*bladed Screws 


Qcsir<mPifch 























132 


MODEL AEROPLANES 


varnish reduced in consistency with turpentine in the 
proportion 2:1. It is, however, more important to 
make the fabric airtight than waterproof. This solu¬ 
tion accomplishes both. Rubber lubricant is made of 
1 part of graphite, 6 parts of pure soft soap, 1 part of 
glycerine, 4 parts of water, and 1 part of salicylic acid, 
boiled together and allowed to cool. 

Making Four-bladed Air-screws, — Fig. 168 on 
the preceding page shows how truly helical and also 
four-bladed screws are carved. Four-bladed screws 
are not so efficient for models as two-bladed ones. The 
drawing also shows the method of marking out and also 
of halving the blocks together at the centre, so that the 
four blades are at right angles to one another. A view 
of an ordinary twin-blade screw of similar design is 
appended to give some idea of the finished shape of the 
blades. The pitch should not exceed the circumferen¬ 
tial measurement of the disc swept by the propeller; 
that is to say, the pitch angle, or the angle made by 
the propeller tip with the axis, should not exceed 45 
degrees. The angles along the blade are determined 
in the manner illustrated by Fig. 168. A line is laid olf 
to any convenient scale equal to the circumference of 
the propeller disc = n r diameter. The tip angle (or 
pitch angle) may now be produced and the triangle 
completed by erecting a line at right angles to the first, 
or the pitch may be erected perpendicularly to the cir¬ 
cumferential line to the spiral scale and the pitch angle 
line drawn in. The circumferential line may now be 
divided into a number of equal parts and the points 
connected up. In the illustration three points have 



GENERAL NOTES 


i 33 


been taken, which will be enough for a small propeller. 
Cardboard templates should be cut to these angles and 
the blades checked at the points corresponding. The 
balance of the screw must be attended to and is a most 
cogent factor in such a small design. Marine-screws are 
exceedingly inefficient when working in air, and their 
use for driving model aeroplanes, etc., is to be strongly 
deprecated. The formula for propeller pitch is: p = . 


Fig. 169.—Securing Wooden Planes 



7 T d. tan A, where p - pitch, tt = 3T4, d = diameter of 
propeller, tan A = tangent of pitch angle. 

Fixing Planes, —Fig. 169 shows a neat and effective 

method of securing the planes. 

Very little wood is now used for the planes of model 
aeroplanes; but to build a plane of veneer, it should 
first be cut to the shape required and then a strip of 
birch pinned and glued on the underside of the leading 
edge for strength. The veneer is then pinned and 
glued to the ribs which have previously been bent to 

O v 

the correct camber. The reader may be reminded that 
birch is the most suitable wood for bentwood pro- 










134 


MODEL AEROPLANES 


pellers, the wood being first cut to shape with a fret¬ 
saw, then soaked in hot water and bent over a bunsen 
burner to the desired pitch. This requires considerable 



Fig. 170.—Geared Motor for Model Aeroplane 

experience, but can be done quite quickly by an ex¬ 
perienced workman. For propellers up to 12 in. in 
diameter, use -rg--in. w r ood; this should gradually taper 
off to ^ in. at the tips. 

Making Motor for Model Aeroplane. —A geared 
motor suitable for a model aeroplane is given by 
Fig. 170. A cage e for the gears A can be made from 
J-in. by ^A-in. strip iron, and the propeller shafts B 
can be made from cycle spokes. The illustration also 
shows a method of fixing the propeller to the 



Fig. 171.—Fixing Shaft of Carved Screw 

shaft. The piece c is soldered to the shaft b, and 
engages with two holes drilled in the propeller boss, 
the propeller being secured by the nut D. The gears 
























GENERAL NOTES 


i35 


A have an equal number of teeth. There is no 
advantage in using a geared-up motor. F is the 
fuselage of the model. 

Fixing Propeller of Model Aeroplane. —With a 
carved propeller, the motor hook can be secured to the 
propeller as in Fig. 171. If a bentwood propeller, the 
best way is to fasten a strip of tin round the centre and 
solder the motor hook to this. 



CHAPTER XYII 


Easily-made Tailless and Box Kites 

One of the difficulties that beset the juvenile kite- 
flyer is the inability to get the kite to rise from the 
ground unless there is a fairly good wind blowing. 
Even then the services of an assistant are required, 
whilst numerous trials to adjust the amount of weight 
on the tail, the position of the carrying thread on the 
kite, and the distance required to be run to get the 
artificial wind to enable the kite to rise above the sur¬ 
rounding buildings, are difficulties that damp the en¬ 
thusiasm of the most inveterate kite-flyer. 

To the kites sold in the shops the foregoing remarks 
apply. They are too heavy, and are suitable for flying 
at the seaside only. To make the sport interesting, 
the kite should fly in the least wind, and should be so 
made as to fly from the hand, the thread or string being 
paid out as the kite rises. It should be perfectly 
balanced so as to be stable in the most erratic wind. 
The kites shown in the accompanying illustrations, if 
made to the directions, will fulfil all the above con¬ 
ditions, and at the same time be easy of construction. 
The dimensions can be varied in proportion; but the 
would-be maker is advised to stick to the given sizes for 
the first attempt. 

The Hargreaves kite (Fig. 172) is the simplest. The 

136 



Fig. 172—Hargreaves Kite Fig. 175.—Box Kite 


* 

> 

/ 5 * 

•_ 72 ‘ „ 

. 



St to* i' ■for' /sp 


• 

vs 

L 



Fig. 176.—Covering with Paper 



Fig. 174.—Measuring Bend Hargreaves Kite 























138 


MODEL AEROPLANES 


frame (Fig. 173) consists of a straight length of yellow 
pine A, to which is attached a cross piece of cane b. 
This cross piece is made by cutting a thin cane and 
splitting it, trimming the edges off until nearly square 
in section, and then bending it over a small gas flame. 
As it gets hot, bend it gently by grasping the ends in 
each hand. Pass it to and fro in the low flame, and it 
w r ill be found to give. Bend it evenly and allow to cool, 
when it will remain in this shape. Find the centre 
and ascertain if the bend is equal on each side by 
measuring as showm in Fig. 174. This being so, notch 
A and b (Fig. 173) slightly where they cross, and 
assemble, applying a little glue and lapping with cotton. 
Join the ends of the bent limb with linen thread, and 
also take a thread round the frame, securing it at each 
extremity in a notch with the addition of glue. 

When dry the frame is covered with paper. The 
very thin coloured paper used for making artificial 
flowers is just the thing. Gum it on with a thin flour 
paste, and allow very little overlap, keeping the paper 
as free from crinkles as possible. Cut a disc of stout 
paper, and gum it over the frame at the crossing. This 
is to strengthen the paper at this point, as the attached 
thread is liable to make a wide hole. Secure a yard of 
strong thread at the crossing, and when dry the kite 
can be tested. If all is right the result will be 
eminently satisfactory, the kite flying from the hand 
like a bird, no tail whatever being needed. 

For decorative purposes a short fish tail and fins can 
be added, or a rubber balloon can be used as a tail. 

The box kite shown by Fig. 175 is not more difficult 



EASILY MADE TAILLESS KITES 139 


to construct than the kite previously described. It 
flies with equal facility, and is quite as steady. Being 
made collapsible it can be rolled in a small compass. 

To make the kite, paste tw T o of the coloured sheets 
together to form a continuous length, and spread on the 
floor. Cut the four uprights of yellow pine to the 
correct length and thickness, and having liberally glued 
them, place them on the paper as shown in Fig. 176, 
and paste a long strip over them on to the paper under¬ 
neath. This is to strengthen the paper round the 
uprights. When dry and firm, which does not take 
long if the glue is put on tacky, the loose end of the 
paper can be joined to the upright to form a hollow 
long box. 

Now cut four thin lengths of wood to form cross 
pieces, secured together with a pin through the centre 
(see Fig. 177). Notch the ends and open them out so 
as to fit inside the box between the uprights. Fit one 
to each end, and then secure the upright ends with a 
linen thread pulled tightly from one to the other, and 
tied and glued at each end. This takes the strain of 
the cross piece off the paper, and at the same time pro¬ 
vides a support for the paper, which is clapped round 
it and gummed on to itself. 

The kite having been completed, a short length of 
thin string is attached about 3 in. from one end of one 
of the uprights. To this the thread for flying is at¬ 
tached. This kite will fly quite well with the thread 
attached to the very end of the upright, so that there 
is no fixed position for it to a fraction of an inch. The 
nearer it is brought to the centre, the more unstable 



140 


MODEL AEROPLANES 


the kite becomes. In a moderate wind, with the 
thread attached to the top, the kite tends to ascend 
more vertical than it would otherwise. 

Fig. 177a shows another simple form of box kite. 
It is made from four strips of straight grained wood 
(preferably spruce), 2 ft. 6 in. by § in. by \ in. Obtain 



Figs. 177 A and B. —Details of Twin Cellular Box Kite 


also four other pieces, each 1 ft. 7J in. long, but tV in. 
wider and thicker than the foregoing, and halve their 
ends to a depth of J- in. by J in., in order that when 
the false end a (Fig. 177b) is tightly bound on, these 
cross sticks will firmly grip the long pieces edgewise; 
the sides of the cell are indicated by dotted lines. It. 
is advisable to make the cross-pieces a trifle long, to 
ensure their straining the kite to its correct form. 
































CHAPTER XVIII 


Building a Model Airship 

It has not for obvious reasons been possible, in the 
design here presented, to rigidly adhere to the lines of 
the prototype, as in the adaptation of the design to 
rubber-driven model form several modifications have 
necessarily been introduced. It has been the aim of 
the writer to bring the model within the constructional 
capabilities of the amateur; indeed, it is hardly possible 
to have simplified the construction further. Now, the 
success of a dirigible, whether full size or model, de¬ 
pends primarily on the observance of the fact that an 
airship is lighter than air, and thus, unlike the aero¬ 
plane, does not rely on speed to obtain lift. Second¬ 
arily, the lifting power of hydrogen must be remem¬ 
bered, and although this varies according to 
temperature and the purity of it, it may be taken as a 
general rule that hydrogen will lift 80 lb. per 1,000 
cubic feet. It is a good rule to adopt a lower figure, 
say 70 lb. lift per 1,000 cubic feet, to allow for dis¬ 
crepancies. In the design here submitted, aluminium 
(or what is equally as good, magnalium) tube forms the 
framework of the body or envelope. The general 
arrangement will be apparent from Figs. 178 and 179, 
which show the model in plan and side elevation re¬ 
spectively. The framework is of hexagonal cross 

T Hi 


14 2 


MODEL AEROPLANES 


section, the longitudinal members of which terminate 
at each end in a brass cap, to which they are riveted 
with soft brass pins. It will be necessary to anneal the 
tubes before bending them to impart the conical shape 
to each end of the frame, and this can best be effected 
in a weak spirit flame, care being taken to keep them 
on the move in it, to obviate fusing them. Where it 
is necessary in the construction to rivet the tubes, 
solder should be run over the pin to take up any play. 
Fig. 180 shows the method of securing the longitudinal 
members to the brass end caps. The tubes are first 
flattened out, as at b, and then riveted to the caps. 
This figure also shows the method of adjusting the 
angle on the rudder. A piece of brass tube is soldered 
to the end cap; and it should be of such a bore that the 
No. 18 gauge wire of which the rudder is constructed 
makes a bare fit through it. Two similar pieces of 
tube, J in. long, are soldered to the rudder, to maintain 
the position of it. Thirteen hexagonal cross members 
will be required, and each is formed from -ft- in. 
aluminium tube. In order that they may not become 
out of truth, they are cross-braced with No. 35 s.w.g. 
piano wire, the ends of each wire being made off in a 
small hole drilled through the tube. Fig. 180 will 
make the detail clear; each cross member is riveted to 
the longitudinal, and the latter is flattened out at those 
points where the cross member is attached. 

The model is driven by four elastic motors, trans¬ 
mitting their power through equal gearing to the twin 
propellers. The four motor rods may, for preference, 
be hollow spars, of the same cross section as the solid 




Fig. 179.—Plan 



























































































































144 


MODEL AEROPLANES 


ones indicated. If such are used, they may be made 
by ploughing a groove in a length of wood of suitable 
cross section so that it represents the letter U. Two 
will be required for each spar, so glued together that a 
hollow tube is formed. At the point where it will be 
necessary to pierce the spar to admit the bracing out¬ 
rigger, small packing pieces of birch should be placed 
in the grooves previous to assembling the two halves 
of the spar. The spars, or, more correctly, motor rods, 
are suspended from the envelope framework by alu¬ 
minium tube outriggers of J-in. diameter. Fig. 181, 
which shows the machine in end elevation, and Fig. 
182, showing the central cross section, indicate the 
form they are to take. Eight of them will be required. 
The angles must be cleanly and accurately formed, so 
that the two centres of thrust lie in the same plane. 
It will be found good practice, when forming both the 
outriggers and the cross-sectional members, to make a 
full-size drawing of them to use as a template. More 
especially is this needed in the construction of the 
cross-sectional members, for the purpose of ensuring 
that, in the operation of embracing them, they are not 
strained in any way so as to become out of truth. 

Fig. 183 shows the joint of the motor-rod outrigger 
to the motor rod itself. As there shown, the tube is 
flattened out partly to engirdle the spar, to which it is 
attached by pinning and clinching. 

The gearing (see Fig. 184) consists of a brass frame¬ 
work (bound to the ends of the motor rods) which pro¬ 
vides bearings for the gears. The use of gears is 
obvious; they eliminate torque on the spars, or the 



I Zd'a* 



Fig. 180.—Joint of Tube to End Caps 



Fig. 181.—End Elevation 




Fig. 183.—Joint of Outrigger to 
Motor Rod 

































146 


MODEL AEROPLANES 


tendency which a single skein would have to twist the 
spar. Pieces of tube are passed over the shafts to bear 
between the gears and the gear bearing. In order to 
counteract the tendency of the rubber hooks to pull out 
straight when the rubber is in tension, the hook ends 
are secured as shown at A. When it becomes neces¬ 
sary to detach the skeins, it is only necessary to slide 
the tubes along the shaft to open the hook. 

In Pig. 185 the kingpost attachment is shown. 
The spar is mortised, the kingpost forced through, 
glue having previously been brushed into the slot, and 
a pin tapped through from the side to secure it. Birch 
should be used for the kingposts, and their widest 
cross section should be f in. by 3 % in., tapering off 
towards the extremities to J in. by in. 

To the ends of each motor rod are attached small 
No. 22 s.w.g. piano wire hooks, to which the spar 
bracing is made fast. A suitable length of wire is 
passed through the spar, and the hooks then formed. 
The bracing is fastened to the kingpost by a couple 
of turns being taken round it. 

Next, four twin hooks should be made, of the form 
shown in Fig. 186. Sixteen gauge wire is to be used 
for them, bent tightly to clip the spar ends, to which 
they are bound. All the hooks should be covered with 
valve tubing to prevent them from cutting through the 
rubber when this latter is in tension. 

The joint of the cross members of the envelope to 
the longeron is given by Fig. 187, from which the bend 
in the longitudinal, hitherto referred to, will be clear. 

To the tail of the machine a pair of superposed 



BUILDING A MODEL AIRSHIP 


147 


surfaces or elevators are fixed. These are fastened at 
their foremost extremities to the motor-rod outriggers, 


A 



Fig. 184 —Arrangement of Gearing 





Fig. 187.—Cross 
Member Joint 


Fig. 186. Detail of 
Twin Hooks 



Fig. 188.—End View of Screw 


and at the rear they are supported by the two cross ribs 
of the rudder. Small slits are to be cut in the fabric 
with which the rudder framework is covered to enable 
any slight alteration in the angle of incidence of the 
elevators to be effected. 

Attention may now be given to the propellers. As 
























































148 


MODEL AEROPLANES 


twin screws are used, they may be made of fairly long 
pitch, since their torques will be opposite and conse¬ 
quently balanced. Fig. 189 gives a perspective view 
of the propeller block marked out ready for carving, 
and Fig. 188 shows the screw in end elevation. The 
screw is first carved as a true helix, and then shaped 
up to the form shown in the sectional view (Fig. 182). 
American white wood should be used for the blocks, 
or, failing this, poplar would do. Circular tin discs are- 
pinned to each side of the propeller boss, to which the 



shaft is soldered. Great care is essential to ensure that 
both propellers are of the same weight, and that each 
is poised; that is, assumes an angle of 180° when bal¬ 
anced on a shaft. They may be finished with a coat of 
gold size and one of varnish. Each gear is driven by 
six strands of J-in. strip elastic, well lubricated with 
soft soa^p and glycerine. 

The covering is to be yellow Japanese silk, proofed 
with varnish diluted with 20 per cent, of linseed oil 
and 10 per cent, of turpentine; two coats should be 
given before the fabric is applied, and two afterwards. 








Fig. 190.—A Model Airship 





















MODEL AEROPLANES 


150 

A covering strip of fabric should be glued over all seams 
to make the envelope as impervious as possible. And 
where the outriggers pass through further pieces should 
be glued over, and flanged on to the tube itself, being 
afterwards well doped. It is well to impress here the 
importance of making the envelope as gasproof as 
possible, and although a fabric entirely impervious has 
yet to be invented, it is possible, with care, to reduce 
loss of gas by percolation to a very low figure indeed. 

A Lucas cycle valve is soldered into the brass end' 
cap constituting the rear of the envelope, for the pur¬ 
pose of inflation, which is effected in the following 
manner: A T-piece is fixed to a cycle pump, and a pipe 
from the gas container to the T-piece. A further tube 
is connected from the remaining arm of the T-piece to 
the valve. To inflate the envelope, release the pressure 
from the container until the pump handle is forced out 
to its full extent, and then shut off pressure and force 
the pump down, thereby causing ingress of gas to the 
envelope. Continue thus until the envelope “ swells.” 
01 course, this method could be adopted if hydrogen 
from the gas jet is used, although this does not possess 
the lifting capacity of hydrogen procured from the 
balloon manufacturers. 

In conclusion, it may be pointed out that the weight 
of the complete model inflated should not exceed 2 lb. 
A view of the appearance of the model in flight is given 
by Fig. 190. 

For those who wish to design model airships of 
their own it may be stated that coal-gas lifts about 
35 lb. per 1,000 cub. ft., or half the weight lifted by 



BUILDING A MODEL AIRSHIP 151 

_ _ 

an equal volume of hydrogen. A small model would 
not be very successful, as the volume, and hence the 
lifting power, decreases as the cube of the diameter. 
Thus assuming a model to be built of half the 
dimensions given in this chapter, the weight of it 
could only bejxixi = i 0 f the original model, 
and it would be found difficult to work to this limit, 
lhe writer would point out that little success can be 
expected from an airship of such small dimensions, as 
the following elementary calculation will show. It 
takes 35,000 cub. ft. of hydrogen to support 1 ton. 


Then 1 cub. ft. of 


hydrogen supports 


2240 

35000 lb 


Now, the cubic contents of a model dirigible, we will 
22 5 5 36 1 

~Y~ X ^2 x ~2 x ~Y x 1728 cub. ft., and 


assume, is 


therefore the total weight it is capable of supporting is 
22 5 5 36 i 2240 

= .026 lb., or .4oz. 


5 

7 x 2 


5 

2 


X 


1728 35000 


From this it will be seen that it is extremely im 
probable that a model can be built to this weight. 

No more suitable covering than gold-beater’s skin 
exists. If the model is of the rigid type, then the 
covering should be stretched over the framework that 
imparts the ichthyoid shape to the envelope. Strips 
of the fabric must be attached with mucilage over all 
seams to make the envelope as impervious as possible. 
It is worthy of note that full-size airships have as many 
as three or four coverings to eliminate loss of hydrogen 
by escape through the pores of the fabric. If, however, 
the reader contemplates building a model of the non- 








152 


MODEL AEROPLANES 


rigid type, a wooden hull should be cut and the fabric 
fitted up to this. The hull should represent the shape 
of the inflated envelope. 

Compressed air also lends itself to model airship 
propulsion. 

In conclusion, a word of warning : do not place the 
model near any fire, gas, match, etc., as any small 
leaks may cause an explosion. 

In building model airships, it is advisable to 
remember that by doublmg the diameter of the 
envelope we get four times the capacity and hence 
four times the lift for only double the weight. This 
will be seen from the following calculation : 

Lift of airship 3 ft. long 2J in. diameter equals, as 
we have just seen, -026 lb. 

By doubling the diameter the calculation becomes: 


22 

7 



36 1 2240 

T * 1728 X 35000 


•052 lb. 


Prom this it will be seen that if it is desired to lift 
a certain weight with a lighter-tlian-air craft, the 
minimum capacity should first be calculated and the 
diameter (which should always be as large as possible) 
then varied to obtain the required capacity. 

Although it has been stated that the lift of 
hydrogen is 70 lb. per 1,000 cub. ft., it will be in order 
to explain two important considerations. It will be 
clear that, firstly, a full-size balloon must be inflated 
to a much higher pressure than a model , owing to the 
heavier mass of material to be forced out to form. As 
a direct adjunct to this fact it will be seen that 
percolation will be high. Consequently the lift weight 






BUILDING A MODEL AIRSHIP 153 


ratio 70 : 1,000 is somewhat a low estimate for a model, 
since, firstly, it will only require to be inflated to less 
than half the pressure of a full-size balloon; and, 
secondly, percolation will be considerably less. The 
writer intentionally gave the full-size limit in order 
that, should the builder’s model fail to come within 
the prescribed limit of 2 lb., its flying capability would 
not be appreciably impaired. 

Further, the envelope is kept to its shape by a 
framework inside, and is consequently full of air. 
Now if we start pumping hydrogen in it will make the 
contrivance heavier instead of lighter, because no outlet 
is provided for the escape of air. This could easily be 
remedied by standing the model on its end with the 
cycle valve at the top, with a valve or tap on the bottom 
brass cap. Open this bottom tap to allow the air to 
escape, and allow the hydrogen to fizz in through the 
cycle valve. Hydrogen will not escape through the 
bottom tap until all the air has been displaced. If the 
hydrogen cannot be had at a high enough pressure to 
operate the valve itself a valve should not be used. 

It may in such a case be necessary to fit an in¬ 
duction valve to the pump. The envelope should be 
inflated to as low a pressure as possible, otherwise the 
lift is correspondingly reduced. In all cases it is 
exceedingly difficult with model airships to prescribe 
any definite formula, and although the lift coefficient 
for models exceeds the figure stated, the conjectural 
nature of the purity (and hence of lift) of hydrogen in 
various parts of the country renders it a safe one to use 
for all practical purposes. 



INDEX 


Action and reaction, 5 
Aerofoil, flow of air round, 10 

-, lift of, 10 

Aeroplane, speed of, 4 

-, types of, 12-16 

-: Why does it fly? 1-11 

A frame, 20, 22, 23 
Air, density of, 35, 36 

- flow, direction of, 5 

- pressure, 2 

Airscrew, action of, 35 
—— balancing 1 , 38 

-, calculations for, 36 

-, efficiency, 35 

-, four-bladed, making, 133 

-, laminated, 39 

-, suitable woods for, 36, 38 


Bamboo planes, 30 
Bending air screws, 42-46 
Biplane, fitting struts to, 128 

-, sample twin-screw, 61-68 

Blade width, maximum, 45 
Bleriot type monoplane, 18 
Box kite, 138, 139, 140 
Bragg-Smith, 15 
Building airship, 141, 154 


Calculations in designing aero¬ 
plane plant, 120 

Camm air-screw, proportions of, 
46 

Canard, meaning of, 8 
Carving air-screws, 35-41 
Chauviere-type airscrew, 38 
Clarke, T. W. K., 14 
Compressed-air engine, 94-102 

- -, container for, 99 

•- -, crank for, 97, 98 

- -, inlet and exhaust, &c., 

of, 97 

--, pistons for, 98 


Compressed-air engine, testing the 
container, 100 

- -, three-cylinder, 94-103 

- -, valve and tap for, 100 

Compressed-air-driven biplane, 
104-114 

-, bracing planes of, 115 

- -, calculations for, 104- 

109 

- -, flying, 118, 119 

-, inter-struts for, 112 

--, materials for, 106 

- -, planes for, 109 

- -, tail for. 111 


Designing, general notes on, 120, 
123 

Dihedral angle, 7 
Double-winder, 70-72 
Drift and lift, 3, 6 


Efficiency airscrew, 35 

- formula, 19 

Elastic motor, disadvantages of, 
94 

Elevator adjustment, 127 
Equilibrium, 2 


Fairey, 12 

Force of gravity, 2 
Forces acting on kite, 2, 3 
Formula, efficiency, 19 
-, type, 18 

Four-bladed air-screws, making, 
133 

Fuselages, 19-34 

--, boat-shaped, 24 

-, box girder, 26 

-, distortion, 30 

-, simple, 28, 29 

-, single spar, 26 


154 
















































INDEX 


i55 


Fuselages, twin-screw, 26 
-, two-membered, 25 

Geared motor for model aero¬ 
plane, 134 

General notes, 124-135 
Gravity and pressure, 6, 7, 8 
Gravity, force of, 2 

Hargreaves kite, 132 
Hollow spar, 22 
Houlberg, 14 
Hydro-biplane, 17 
Hydro-monoplane, 87-93 

-, bearings for, 88 

-, elevator for, 90 

-, floats for, 90 

-, fuselage for, 87 

-, mainplane for, 88 

-, weight of, 93 

Hydroplane floats, calculating 
capacity of, 130 
-, water surface, 128 

Kite, box, 138, 139, 140 

-, forces acting on, 2-3 

-, Hargreaves’, 132 

-, speed of, 4 

-, tailless, 136-141 

Lateral stability, 7 
Lift and drift, 3, 6 

- of aerofoil, 10 

Loading, 44 

- for aeroplanes, 127 

Longitudinal stability, 8 
Lubricant, 125 

* 

Mann, R. f., 20 
Materials, choice of, 28 
Monoplane, Bleriot type, 18 

-, collapsible, 73-79 

-- --, chassis for, 78 

-, -, mainplane for, 75 

-, -, propellers for, 79 

-, -, tail for, 74 

-, hydro, 87-93 

-, Ridley, 12 

-, -, twin-screw, 54-60 

-, -, mainspar for, 54 

-, -, propellers for, 58 

-, tractor, 80-86 (see Tractor 

monoplane) 


Penaud, Alphonse, 94 
Piano wire, uses of, 30 
Pitch, 35, 36, 39, 42, 44, 45 

- angles, setting out, 40 

“Plane” and “aeroplane,” mean¬ 
ing of terms, 8 
Planes, bamboo. 30 

-, cane, 50 

-, constructing, 47-53 

-, fixing, 133 

-, swept back, 52 

-, types of, 47 

-, umbrella ribbing, 50 

-, wire, making, 50, 51 

——, wooden, 48 

Plant, calculations for designing, 
120 

Pressure and gravity, centres of, 
6, 7, 8, 


Resistance, air, 3 
Ridley monoplane, 12 


Scale-models, building, 32, 34, 121, 
122, 123 

Silk, waterproof, 130 
Skid, fitting, 126 
Slip, 35 

Small biplane, driving, 102-103 
Spar sections, 26, 27 
Speed of aeroplane, 4 
Spindles, attaching, 46 
Stability, 29, 124, 125 

-, lateral, 7, 42 

-, longitudinal, 8 

Tailless kites, easily made, 136- 
141 

T frame, 20, 22. 23 
Thrust, 42 

-required for aeroplane, 11 

Timber, strength of, 29, 30, 32 
Torque, 29, 36, 42 
Tractor hydro-biplane, 17 

I -, monoplane, 80-86 

; - , chassis for, 82 

- -, mainplane for, 84 

--, mainspar for, 80 

-- -, twin-gears for, 84 

Twining, E. W., 14, 17 
-airscrew, 46 





























































INDEX 


156 


Twin-screw biplane, simple, 61-68 

- - , elevator for, 62 

- - , flying the, 66-68 

-- , mainspar for, 61 

Type formula, 18 
-of aeroplanes, 12-18 


Waterproof silk, 130 
Water-surface hydroplane, 128 
Winders for elastic motors, 69-72 

-, double, 70-72 

-, push-in-the-ground, 69-70 

Wing bracing, 30 


Printed by Cassell & Company, Limited, La Belle Sauvage, London, E.C.4 

50.220 


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